For this exercise, it seems the person who drew the graph misunderstood the given situation. First of all, if you do not buy any shirts, the cost is 0 so the graph should start from the origin. Also, it is given that the first five shirts cost $$ 12.99$ each. This means we would add $12.99$ to our total cost for each shirt purchased.

Number of shirts purchased ( $n$ )	$12.99 n$	Cost
$0$	$12.99 \cdot 0$	$0$
$1$	$12.99 \cdot 1$	$12.99$
$2$	$12.99 \cdot 2$	$25.98$
$3$	$12.99 \cdot 3$	$38.97$
$4$	$12.99 \cdot 4$	$51.96$
$5$	$12.99 \cdot 5$	$64.95$

The table above shows that we should see a constant increase between $0$ and $5$ shirts. The given graph does not coincide with this as it shows a horizontal line. It is likely that the person interpreted this part of the situation to be " $5$ shirts cost $12.99 .$ " At this point, we have the following graph.

Each shirt after the fifth costs $4.99$ each. This means that we have to add $4.99$ to the cost of the first five shirts every time we purchase another shirt. This is shown in the table below.

Number of shirts purchased ( $n$ )	$4.99 (n - 5) + 64.95$	Cost
$5$	$4.99 (5 - 5) + 64.95$	$64.95$
$6$	$4.99 (6 - 5) + 64.95$	$69.94$
$7$	$4.99 (7 - 5) + 64.95$	$74.93$
$8$	$4.99 (8 - 5) + 64.95$	$79.92$
$9$	$4.99 (9 - 5) + 64.95$	$84.91$

Again, the given graph does not coincide with this piece of information. The vertical drop in the given graph shows a decrease in price from $5.99$ to $4.99,$ but the $y -$ axis is supposed to reflect the total cost of the shirts so it should increase but at a slower rate.

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