Larry Barrett
A square with a 2-digit area must have a side = 4, 5, 6, 7, 8, or 9.

To find the length of the crease if bottom right corner is folded to the mid-point of the top side, without actually folding the paper, I can see that this crease will bave a length bewteen the length of a crease if the bottom right corner is folded to the top right corner (crease = side) and the length of a crease if the bottom right corner is folded to the top left corner (crease = side x sqrt2).

So, side diagonal
.......4.........5.66
.......5.........7.07
.......6.........8.49
.......7.........9.90
.......8........11.31
.......9........12.73

If the crease to the mid-point must be an even number, it must be 6, 8, or 10.
I don't see an algebraic way to determine this so am guessing that the length will be about halfway between the side and the diagonal, so guessed 6 (square with side 5).