Question 121726
Your problem is either subtracting fractions or taking fractions to a fractional power. 
We can look at both. 

{{{1/8-2/3}}}
Subtractng fractions.
Whenever you add or subtract fractions you need to have the same denominator.  
The easiest way to get a common denominator is to make it the product of your two denominators.
{{{D=8*3=24}}}
Now find each fraction as an equivalent fraction with denominator of 24.
{{{1/8=x/24}}}
{{{24*(1/8)=x}}}
{{{x=3}}}
{{{1/8=3/24}}} 
and
{{{2/3=y/24}}}
{{{24*(2/3)=y}}}
{{{y=16}}}
{{{2/3=16/24}}}
Now you can subtract.
{{{1/8-2/3=3/24-16/24}}}
{{{1/8-2/3=(3-16)/24}}}
{{{1/8-2/3=-(13/24)}}}

Taking fractions to a fractional power. 
{{{(1/8)^(-2/3)}}}
You can also look at 1/8 as {{{8^(-1)}}}.
{{{(1/8)^(-2/3)=(8^(-1))^(-2/3)}}}
From your exponentiation rules,
{{{(x^M)^N=x^(M*N)}}}
Then
{{{(1/8)^(-2/3)=(8^(-1))^(-2/3)}}}
{{{(1/8)^(-2/3)=(8)^(2/3)}}}
{{{(1/8)^(-2/3)=(2)^(2)}}}
{{{(1/8)^(-2/3)=4}}}