Dots sells a total of 267 t-shirts ($2) and shorts ($3). in april, total sales were $633.

how many t-shirts and shorts did dots sell?

Lets 
s = # of shorts sell
and
t = # of shirts sell

s + t = 267 so s = 267 - t
3s + 2t = 633

substitute s = 267 - t     into   3s + 2t = 633

3s + 2t = 633
3(267 - t) + 2t = 633
801 - 3t + 2t = 633
-t = -168
t = 168

s = 267 - t
s = 267 - 168
s = 99

answer
shirts = 168
shorts = 99

A= b/2 because u simplying both sides of equation