because this is a right triangle, you can use the pythagorean theorem: a^2 + b^2 = c^2, where a and b are legs and c is the hypotenuse.
you have a leg, 18, and the hypotenuse, 26. plug those in:
18^2 + b^2 = 26^2 ... evaluate exponents
324 + b^2 = 676 ... subtract 324
b^2 = 352 ... square root both sides
b = √(352)
b = 18.76
