The graph below shows the cost of pens based on the number of pens in a pack. What would be the cost of one pen? A graph is shown with title Purchase of Pens. The horizontal axis label is Number of Pens, and the vertical axis label is Cost in dollars. Points are plotted on the ordered pairs 3, 4.50, and 5, 7.50 and 7, 10.50.

(3 points)

a
$1.50
b
$2.30
c
$6.00
d
$13.50