Did I find the diagonal of a rectangle correctly?

The diagonal of a rectangle is 25 cm.
a. Find the dimensions of the rectangle if it is 5 cm longer than it is wide.
My answer…
w=width
w+(w+5)^2=25^2

w=15

w+5=20

Question b. What are the dimensions if the rectangle is a square?

s=length of each side
s^2+s^2=25^2
s^2=625/2

That’s how far I got and I’m confused what the answer might be. I don’t know how to get to that final step. Please help.