-3/5[2-3-1/2(3/4-1/2)]

Do what is in the innermost parentheses first.

-3/5[2-3-1/2(3/4-1/2)]

When in the innermost parentheses
Do the first exponential first.  There are none
Do the first multiplication or division going left to right.

The first multiplication we come to is a division 3/4
We divide 3 by 4 and get 0.75. So we replace 3/4 by 0.75

-3/5[2-3-1/2(0.75-1/2)]

We start over. We do what is in the innermost parentheses first.
When in the innermost parentheses
Do the first exponential first.  There are none. So we
Do the first multiplication or division going left to right.

The first multiplication or division we come to is a division 1/2
We divide 1 by 2 and get 0.5. So we replace 1/2 by 0.5

-3/5[2-3-1/2(0.75-0.5)]

We start over. We do what is in the innermost parentheses first.
When in the innermost parentheses
Do the first exponential first.  There are none. So we
Do the first multiplication or division going left to right.
There are none. So we do the first addition or subtraction
going left to right.

The first addition or subtraction we come to is a subtraction 
0.75-0.5. So we subtract and get 0.25. So we replace 0.75-0.5
by 0.25

-3/5[2-3-1/2(0.25)]

We start over. We do what is in the innermost parentheses first.
The innermost parentheses (0.25) has nothing to do in it.
So we go to the next innermost parentheses [2-3-1/2(0.25)]
There are no exponents.  So we do the first multiplication
or division we come to left to right. That is the division
1/2, so we replace 1/2 by 0.5

-3/5[2-3-0.5(0.25)]

We start over. We do what is in the innermost parentheses first.
Again, the innermost parentheses (0.25) has nothing to do in it.
So we go to the next innermost parentheses [2-3-0.5(0.25)]
There are no exponents.  So we do the first multiplication
or division we come to left to right. That is the multiplication
0.5(0.25) so we replace that by 0.125

-3/5[2-3-0.125]

We start over. We do what is in the innermost parentheses first.
The innermost parentheses is [2-3-0.125].
So we go to the next innermost parentheses [2-3-0.5(0.25)]
There are no exponents.  So we do the first multiplication
or division we come to left to right. That is the multiplication
0.5(0.25) so we replace that by 0.125

-3/5[2-3-0.125]

We start over. We do what is in the innermost parentheses first.
The innermost parentheses is [2-3-0.125]. There are no exponents,
mutiplicatrion or division in the parentheses, So we do the first
 addition or subtraction we come to left to right. That is the 
subtraction 2-3, so we replace 2-3 by -1

-3/5[-1-0.125]

We start over. We do what is in the innermost parentheses first.
The innermost parentheses is [-1-0.125]. There are no exponents,
mutiplications or divisions in the parentheses, So we do the first
 addition or subtraction we come to left to right. That is the 
subtraction -1-0.125, so we replace -1-0.125 by -1.125

-3/5[-1.125]

We start over.  There is nothing to do in the parentheses. There are
no exponents. So we do the first multiplication or division we come
to.  This is -3 divided by 5. So we replace -3/5 by -0.6

-0.6[-1.125]

The only thing left is this multiplication, so we do it and get

0.675

If you do it with fractions instead of decimals you get 27/40

Edwin