How to find the side of a right triangle if given two side's measures

How do I find the measure of a side of a right triangle if I am provided with two sides?

One leg measures 20 units and the hypotenuse measures 25 units, and it is a right triangle.
Answer please? Also explain how you found this and if there's a formula for it. Thanks!

The formula is a^2 + b^2 = c^2. The two legs are a and b and the hypotenuse is c.

So,

20^2 + b^2 = 25^2

400 + b^2 = 625

b^2 = 225 now take the square root of each side to get

b = 15

a^2 + b^2 = c^2

c = hypotenues
a and b = legs

a^2+b^2=c^2

so 20^2+b^2=25^2