One page = $0.008
85 Pages = $0.008 x 85
= $0.68
120 Pages = $0.008 x 120
= $0.96
100 Pages = $0.008 x 100
= $0.8
Differences between printing 120 pages and 100 pages : the cost of printing 120 minus the cost of printing 100 pages
$0.96 - $0.8 = $0.16