The top of the flag pole touched the ground 12 feet from the base.
Since it cracked 9 feet from the base, 9 is the vertical leg of the right triangle formed. The rest of the flagpole, 24-9=15, is the hypotenuse, as it is slanted down to the ground. The missing side is the horizontal leg, which we will call b:
9²+b²=15²
81+b²=225
Subtract 81 from both sides:
81+b²-81=225-81
b²=144
Take the square root of both sides:
√b²=√144
b=12