Find $m$ and $n$ Two finite sets have m and n elements. Thew total number of subsets of the first set is 56 more than the two total number of subsets of the second set. Find the value of $m$ and $n$.

The equation to this question will be $2 ^ m$ - $2 ^ n = 56$.

But I don't know how to solve this equation.

Let $k = m-3$ and $l=n-3$, then 
$$
2^k-2^l = 56/2^3 = 7.
$$
Now determine the values of $k$ and $l$.
