We can use the Pythagorean Theorem to solve this:
a^2 + b^2 = c^2 ( a and b are the sides and c is the hypotenuse)
We can fill in what we know and solve:
36^2 + b^2 = 85^2
1296 + b^2 = 7225
b^2 = 7225 - 1296
b^2 = 5929
b = SQRT(5929)
b = 77
The other leg is 77 meters long