Equation with Variables in Exponents

The problem is: Solve the equation 22x-1  =  8x + 7
and the answers are:

a) -22
b) 22
c) -8
d) 8

The answers I keep getting are 2 or 5 

22x - 1 = 8x + 7
22x – 1  = 23(x + 7)  {get a common base of 2.....8 is 23}
2x - 1 = 3(x + 7) {since you have the same base, set exponents equal}
2x - 1 = 3x + 21 {distributive property}
x = - 22 {subtract 2x and subtract 21 from both sides} 

– Algebra House