The graph y=|x|-4 is obtained from the graph y=|x| dy <span>moving down 4 units the graph y=|x| along the y-axis (see, if x=0, then for y=|x|, y=0 and for y=|x|-4, y=-4).
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These two graphs have the same form.
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You can buy 4 shirts because you bought one pair of jean (80 - 29 = 51) and so with the leftover money you could buy 4 shirts because (12 x 4 = 48) and then you'd have a leftover 3 dollars.