x = jeans
y= shirts
29x + 12y = 80
you can only buy one pair of jeans so let x=1 and then solve for y to determine the amount of shirts you can buy
29(1) + 12y = 80
29 +12y = 80
12y = 51
y= 4.25
since you can't buy 1/4th of a shirt, you drop the decimal
you can buy 4 shirts.