Mondays: 7 * 1.5 = <<7*1.5=10.5>>10.5
Tuesdays: 9 * 2.5 = <<9*2.5=22.5>>22.5
22.5 - 10.5 = <<22.5-10.5=12>>12 cm
It rained 12 centimeters more on Tuesdays than on Mondays.
#### 12