Answer:
350
Explanation:
If x is the number of hamburgers and y is the number of cheeseburgers, then:
x + y = 764
y = x + 64
Solve the system of equations with substitution or elimination. Using substitution:
x + x + 64 = 764
2x + 64 = 764
2x = 700
x = 350
350 hamburgers were sold.