A two-digit number N has the following property: If you reverse the digits of N, you get M. Then M + N is a perfect square.

How many possible values of N are there?

Can anyone help on this? I don't know how to start.

Let the first digit be f and the second be s.

Then N = 10f + s and M = 10s + f, so M+N = 11(f+s)

For this to be a perfect square we must have f + s = 11, so find all the digits, f and s that sum to 11.