350 hamburgers were sold on the Sunday.
Step-by-step explanation
Suppose, the number of hamburgers sold on the Sunday was

As there were 67 more cheeseburgers sold than hamburgers, so the number of cheeseburgers sold

Given that, the total number of hamburgers and cheeseburgers sold was 767. So, the equation will be.....

So, the numbers of hamburgers sold on Sunday was 350.