Mondays: 7 * 1.5 = 10.5. Tuesdays: 9 * 2.5 = 22.5. 22.5 - 10.5 = 12 cm. It rained 12 centimeters more on Tuesdays than on Mondays.
The answer: 12
Reverse engineering the question: On each of 7 Mondays, it rained 1.5 centimeters. On each of 9 Tuesdays it rained 2.5 centimeters. How many more centimeters did it rain on Tuesdays than Mondays?

He buys the silver for 1.5 * $20 = $30. He bought 1.5 * 2 = 3 ounces of gold. The gold is worth %20 * 50 = $1000 per ounce. So he buys 3 * $1000 = $3000 on gold. So he spent $30 + $3000 = $3030 on everything.
The answer: 3030
Reverse engineering the question: John buys 1.5 ounces of silver and twice as much gold. The silver costs $20 per ounce. The gold is 50 times more expensive per ounce. How much does he spend on everything?

The weight of 12 crates of vegetables is 12 * 4 = 48 kilograms. The weight of 16 cartons of vegetables is 16 * 3 = 48 kilograms. So the total weight of all crates and cartons is 48 + 48 = 96 kilograms.
The answer: 96
Reverse engineering the question: A store transports fresh vegetables in crates and cartons using its delivery truck. One crate of vegetables weighs 4 kilograms and one carton 3 kilograms. How much will a load of 12 crates, and 16 cartons of vegetables weigh?

He buys 10 / 1.25 = 8 notepads. That means he buys 8 * 60 = 480 pages.
The answer: 480
Reverse engineering the question:
Bart buys $10 of notepads for $1.25 each. They have 60 pages each. How many pages did he buy?