An Internet store charges a base fee plus $1.50 per pound to ship items. The table shows samples of their shipping rates.

Shipping Rates
Weight of Package
(pounds)
Shipping Cost
(dollars)
2
8.00
5
12.50
7

9
18.50
10

17
30.50

Derek wants to ship items that weigh a total of 7 pounds, and Keisha wants to ship items that weigh a total of 10 pounds. How much more does Keisha pay for shipping than Derek?