350 hamburgers were sold on the Sunday.
Explanation
Suppose, the number of hamburgers sold on the Sunday was [tex]x[/tex]
As there were 67 more cheeseburgers sold than hamburgers, so the number of cheeseburgers sold [tex]=x+67[/tex]
Given that, the total number of hamburgers and cheeseburgers sold was 767. So, the equation will be.....
[tex]x+(x+67)= 767\\ \\ 2x= 767-67\\ \\ 2x=700\\ \\ x= \frac{700}{2}=350[/tex]
So, the numbers of hamburgers sold on Sunday was 350.