The x inside the parentheses has its exponent -3 showing.
The 4 inside the parentheses has the exponent 1 but it 
is not showing, so let's give it a 1 exponent that shows:



Next we will remove the parentheses by using the distributive
principle of exponents.  That is we multiply each exponent
that is inside the parentheses, the 1 and the -3,  by the exponent
just outside the parentheses, the -4.  So we get:



or



Now to make the exponent -4 positive, we move the base and exponent
to the denominator and change the sign of the exponent to positive:



Finally we write  as 256



Edwin