As seen in the badly drawn picture attached in this question we are trying to find the point at the top of the ladder and the point at the bottom of the ladder. As seen in the picture ground level has an altitude of 0 ft meaning that lower than this would be in the negatives. Since the basement floor is 12 feet below ground level then this point would be -12 ft. Now since we know that the ladder is 29ft tall we simply add this height to the basement floor value to get the value of the 2nd floor ceiling (top of the ladder).
29ft + ( -12ft) = 17ft
Therefore we can see that the point at the top of the ladder is 17ft.
