Start by writing an equation with two unknown variables
x= number of cheeseburgers
y=number of fries
write the equation as a linear equation
graph the equation and see all the points that lie in the line
The points with a whole solution on x and y are the possible combination Ms. Mendoza can do.
the possible combinations could be
0 hamburgers asn 12 fries.
2 hamburgers and 9 fries.
4 hamburgers and 6 fries.
6 hamburgers and 3 fries.
8 hamburgers and 0 fries.