Hey there! I'm happy to help!
Let's call the hamburgers h and the cheeseburgers c.
h+c=810
c=h+60
Let's plug this value of c into the first equation to solve for h.
h+h+60=810
2h+60=810
Subtract 60 from both sides.
2h=750
Divide both sides by 2.
h=375
Therefore, 375 hamburgers were sold on Wednesday.
Have a wonderful day! :D