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A local hamburger shop sold a combined total of 577 hamburgers and cheeseburgers on Thursday. 
There were 73 fewer cheeseburgers sold than hamburgers. How many hamburgers were sold on Thursday?
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What you are given is this:
h + c = 577,   (1)     (h = # of hamburgers,  c = # of cheeseburgers)
h - c =  73.   (2)
Add equations 1) and (2) (both sides). You will get
2h = 650.   Hence,   h =  = 325.  This is the number of hamburgers sold.
Now find yourself the number of cheeseburgers.
 = 325.  This is the number of hamburgers sold.
Now find yourself the number of cheeseburgers.