Carol H. answered 03/25/18
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Draw a picture and you will see that you have a right triangle and can use the Pythagorean Theorem.
Let x = the length of the ladder
Let x - 8 = the distance from the ground to the top of the ladder
a2 + b2 = c2
162 + (x - 8)2 = x2
256 + x2 - 16x + 64 = x2
-16x = -320
x = 20 feet