A man spends 1/9 of his salary on rent, 1/2 on food, and 1/4 on clothes. If he has 20 dollars left at the end of the month, how much does he earn?
Let T be the total amount he earns....so....
T - (1/9)T - (1/2)T - (1/4)T = 20 common denominator = 36
(36/36)T - (4/36)T - (18/36)T - ( 9/36)T = 20
(5/36)T = 20
T = 20 ( 36/5) = $144
+318 
