You can solve this using the Pythagorean theorem which states that the square of the length of the hypotenuse is the sum of the square of the lengths of the two legs. In equation form:
c2 = a2 + b2
If the third side is b,
b2 = c2 - a2
b = sqrt(c2 - a2)
Using the given values:
b = sqrt (65^2 - 60^2)
b = 25 in
