Answer:
4 can be rewrite as 2•2, and that's the same as 2².
8 can be rewrite as 2•2•2, and that's the same as 2³
So we can rewrite the whole expression as:
2^x = (2²)⁸•(2³)⁴
2^x = 2¹⁶•2¹²
2^x = 2²⁸
So x = 28
