2 * 3^(X + 1) - 3^X = 15
2 * 3 ^X* 3 - 3^X = 15
3^X * ( 2 * 3 - 1 ) = 15
3^X * 5 = 15
3 ^ X = 3 ^ 1
X = 1
................................................................
4 ^ (X + 1) + 4 ^ X = 320
4 ^X * 4 + 4 ^ X = 320
4^X * ( 4 + 1) = 320
4 ^ X = 64
4 ^ X = 4 ^ 3
X = 3
...............................................................
3 * 5 ^ (X + 3) + 2 * 5 ^ ( X + 1 ) = 77
3 * 5^X * 5^3 + 2 * 5 ^X * 5 = 77
5^X * 5 * ( 3 * 5^2 + 2) = 77
5 ^ (X+1) * 77 = 77
5 ^ (X + 1) = 1
5 ^ ( X + 1 ) = 5 ^ 0
X + 1 = 0
X = ( - 1 )