Kaixuan gave 1/4 of his money to his mother. He spent 5/18 of the remainder on a wallet and 2 t - shirtsand had $312 left. The wallet cost 4 times as much as a t-shirt. (a) How much did Kaixuan have at first? (b) How much did each t-shirt cost?

(m-m/4) (1-5/18) = 312

[ (4m-m) / 4] (13/18) = 312

(3m/4) (13/18) = 312

39m/72=312

39m=22464

m=576

So Kaixuan had $576 to start with.

...

w=4t

(3m/4) (5/18) = w+2t

15m/72=w+2t, using w=4t and m=$576 we have:

15 (576) / 72=4t+2t

8640/72=6t

120=6t

t=$20

So each t-shirt costs $20.