See picture for explanation.
One equation with 3 variables cannot be solved in the sense that you can find "the" 3 values for x, y and m. You can observe that this equation represents a family of straight lines with varying slope (depending on m).
6 1/4 - 5 1/2=
6 1/4 - 5 2/4= 3/4
The answer is 3/4.