let t = the total number of hamburgers and cheeseburgers, c = the total number of cheeseburgers, and h = the total number of hamburgers.
t = c + h where t = 600
c = h + 50
Use substitution to solve for h:
600=(h+50)+h
600= 2h+50
600-50=2h
550=2h
550/2=2h/2
h=275
therefore, 275 hamburgers were sold on thursday.