sold = t
hamburgers = h
cheeseburgers = c
h + 3h = t
h represents the amount of hamburgers. 3h is equivalent to c, since we know that the number of cheeseburgers cold was three times the number of hamburgers sold. We add the two because it is a combined total.
Now we input the value for t, which is the total number of hamburgers and cheeseburgers sold, which is 516.
h + 3h = 516
Now you can solve for h.
Add the h to 3h,
h + 3h = 516
which gives you:
4h = 516
Divide both sides by 4, which gives you:
h = 129.