A 25 foot ladder is placed against a vertical wall with the foot
of the ladder seven feet from the wall. The foot of the ladder slides so
that the top of the ladder slips to a level four feet less than before.
How far did the foot of the ladder slide away from the vertical wall.
The height of the shaded triangle is 24. So, the distance that foot
of ladder slid equals the base of the lower triangle minus 7 feet i.e.,
Interpreting question as asking how far did the foot of the ladder end
up from the vertical wall is also reasonable under this interpretation,
15 feet would be the correct answer.
Either answer would be counted as correct.