ax + by = c using 7 and 8 for integers
solve the equation using the elimination method
You have ONE equation with TWO unknowns. In order
to use elimination, you need TWO equations with
two unknowns. That allows you to manipulate the
equations so that the co-efficient of one of the
unknowns is the same (as far as absolute value)
in both equations. Then, you either add or subtract
the two equations, leaving ONE equation with ONE
unknown. You solve for that unknown and substitute
the value into one of the original equations to
solve for the second unknown.
The phrase "using 7 and 8 for integers" doesn't help.
7 and 8 are, indeed, integers, but there is no way
to determine where they are used in your equation.
In fact, there is no guarantee that they will appear
anywhere in the process of working out a solution, if
we had a second equation to use in this problem.