Given: A local shop sold 320 cheeseburgers and hamburgers combined
To Determine: The number of hamburgers sold if the number of cheeseburgers sold was three times the number of hamburgers
Solution
Let x represents the number of cheeseburgers sold and y be the number of hamburgers sold
Therefore

Also, the number of cheeseburgers sold was three times the number of hamburgers

Let us combine the two equations


Substitute the y into equation 1

Hence, the number of hamburger sold is 80