Set up an equation like this, where n represents the number:
2(n + 6) = 3(n - 6)
2n + 12 = 3n - 18
-n + 12 = -18
-n = -30
n = 30
The number is 30. You can even double-check by plugging 30 into each side of the original equation and simplifying:
2(n + 6) = 3(n - 6)
2(30 + 6) = 3(30 - 6)
2(36) = 3(24)
72 = 72
Check.
