Instead of doing yours for you, I will change the numbers,
do it step by step.  Then you can use it as a model to do 
yours exactly the same way step by step:

Write 
4x + 5y = 21

Take out the y and put in (-3x + 4) in place of it

4x + 5(-3x + 4) = 21

Remove the parentheses by distributing the "+ 5" times
the "-3x", getting "- 15x" and also multiplying the "+ 5"
times the "+ 4" getting "+ 20", so write "- 15x + 20"
in place of + 5(-3x + 4)

4x - 15x + 20 = 21

Combine the "4x - 15x" as -11x, so write -11x instead of 
"4x - 15x":

    -11x + 20 = 21

Add - 20 to both sides:

 -11x + 20 - 20 = 21 - 20

The + 20 and the - 20 cancel out on the left,
so we just have -11x on the left. On the right
we replace the 21 - 20 by 1

          -11x = 1

We divide both sides by -11

         

Then the -11's cancel, and the right side becomes .

So that means 

         

Now we take the original second equation:

         y = -3x + 4

And we substitute  for x

         y = -3 + 4

Multiply the -3 by the , getting 

         y =  + 4

Get the least common denominator which is 11 by multiplying
the +4 by  which just amounts to multiplying by 1:

         y =  + 4

So we have

         y =  + 

or

         y = 

So the solution is (x,y) = 

Now do yours exactly the same way.

Edwin