It should be 12 ft away from the wall. Not 4 ft. You do not just subtract the difference because as you pull it away from the wall, the ladder is mostly moving horizontally with only a small vertical change.
You can use Pythagorean Theorem to find the answer. Think of the ladder as the hypotenuse of a right triangle with the wall and the ground as the legs.
To determine the factor pairs for the number 30, simply find out the smallest set of numbers that will multiply to give 30, you would need to break down composite numbers to do this.
30 = 6 • 5 = 2 • 3 • 5.
These all are prime numbers that when multiplied together equals 30.
