Question 5856
The ladder, wall, and ground form a right triangle.  The ladder is on the hypotenuse.  Let c=26 and a=10 (note: 2 is squared)

a2 + b2 = c2

10(2) + b2 = 26(2)

100 + b2 = 676
-100

b(2) = 576

b=24 squared

I hope that helps you