Answer:
The number of hamburgers sold was 126.
Explanation:
Let h = number of hamburgers sold
let c = cheeseburgers sold
c+h = 378
c = 2h
Substitute c =2h into c+h =278
c+h =378
2h+h = 378
Combine like terms
3h = 378
Divide by 3
3h/3 =378/3
h =126
The number of hamburgers sold was 126.