Use the Pythagorean theorem to calculate the distance from the wall the ladder originally is:
x = sqrt(30^2 - 24^2)
x = sqrt(900-576)
x = sqrt(324)
x = 18
The ladder was originally 18 feet from the wall. Moving the ladder 3 feet further away makes the new distance 18 + 3 = 21 feet.
Now use the Pythagorean theorem again to find the new height of the ladder.
Height = sqrt(30^2 - 21^2)
Height = sqrt(900 - 441)
Height = sqrt(459)
Height = 21.42
Rounded to the nearest tenth = 21.4 feet.
