a^m * a^n = a^(m + n)
a^0 = 1 (a<>0)
2^(x + 3) - 12*2^(x - 2) = 20
2^(x - 2)*(2^5 - 12) = 20
2^(x - 2)*(32 - 12) = 20
2^(x - 2) = 1
x - 2 = 0
x = 2
