Consider the following 4x4 grid :
972 9 5 55 18 22 x 28 50 24 25 26 7 400 52 4
Find $x$. However, as the title suggests, there are multiple solutions. You have to find them all and explain why.
Bonus question: Multiple grids can give the same set of solutions. Find how many different grids have the same solutions as the grid above.
The number of solutions is somewhere between 6 and 17.
This might be related to magic squares
Hint #3 (this one helps a lot, but you can still solve the puzzle without seeing this hint. If you want a real challenge, don't look at this one.):
My 4x4 grid was entirely created using the magic square in hint#2.
More hints will be given over time.