Paul bought 9 total shirts for a total length f $72. Tee shirts cost $10 and long sleeve shirts cost $7. How many of each type shirt did he buy

6 long sleves and 3 short

X = tee shirts, y = long sleeved shirts

x + y = 9 ... x = 9 - y

10x + 7y = 72

10 (9 - y) + 7y = 72

90 - 10y + 7y = 72

-10y + 7y = 72 - 90

-3y = - 18

y = - 18/-3

y = 6 < = = = 6 long sleeved shirts

x + y = 9

x + 6 = 9

x = 9 - 6

x = 3 < = = 3 tee shirts