We are 4 eigth graders from Fayette County West Virginia.
(Brittni, Bridgette, James, and Jessica)
We found a different solution to the Mystery Op 4.
If you subtract one from the first digit,
then multiply it by the second digit,
then add what you got when you subtracted one from the first digit, you get the solution.
y = first digit
z = second digit
(y - 1) * z + (y - 1) = solution
For example: (6 - 1) * 2 + (6 - 1) = 15