do you mean 5*(20/4)^2 or (5*(20/4))^2?
because if you mean 5*(20/4)^2, then you would square the 20/4 first (so 5, which is 25 to the power of 2). then 25 times 5 is 125.
but if you mean (5*(20/4))^2, then you would multiply the 5 with (20/4), which is 25, and then square the 25, which would be 625.