Do you mean 7x(13-5) = 8^2 ?
first do the parentheses like this:
7x(8) = 8^2
on the left you can put the 7 and 8 together like this:
56x = 8^2
8^2 just means 8 * 8 like this:
56x = 64
divide both sides by 56 to get the x by itself like this:
x = 64/56
reduce
x = 32/28
x = 16/14
x = 8/7
Answer: x = 8/7