Camilla needs 12 / 3 = 4 batches of pizza dough. 4 batches of pizza would require 30 x 4 = 120 minutes. Camilla needs to bake the pizzas 12 / 2 = 6 times. 6 times in the oven would take 30 x 6 = 180 minutes. Altogether, it would take 120 + 180 = 300 minutes to finish making 12 pizzas. 300 minutes is 300 / 60 = 5 hours.
The answer: 5
Reverse engineering the question: It takes 30 minutes to make pizza dough and another 30 minutes in the oven for the pizza to cook. If one batch of pizza dough can make 3 pizzas but the oven can only fit 2 pizzas at a time, how many hours would it take for Camilla to finish making 12 pizzas?

He gained 2 * 3 = 6 inches. So his height is 66 + 6 = 72 inches. So he is 72 / 12 = 6 feet tall.
The answer: 6
Reverse engineering the question: John was 66 inches tall. He had a growth spurt and grew 2 inches per month for 3 months. How tall is he in feet?

There are 750 * 4 = 3000 red jelly beans. There are 3000 / 3 * 4 = 4000 jelly beans in the jar.
The answer: 4000
Reverse engineering the question: There are some jelly beans in a jar. Three fourths of the jelly beans are red, and one quarter of the red jelly beans are coconut flavored. If 750 jelly beans are coconut flavored, how many jelly beans are there in the jar?

900 x 3 / 4 = 675 people came before the start of the concert. 900 - 675 = 225 people did not come before the start of the concert. 225 x 5 / 9 = 125 people came few minutes after the first song. So, 125 + 80 = 205 people came to the concert that was not able to be at the start of the concert. Therefore, 225 - 205 = 20 people did not go to the concert.
The answer: 20
Reverse engineering the question:
Nine hundred tickets were sold to a concert. Three-fourths of those who bought the ticket came before the start of the concert. Five-ninths of the remaining came few minutes after the first song. Eighty people arrived during the middle part of the concert while the rest did not go. How many of those who bought the tickets did not go?