Tom is currently two times older than Ann, which means he is 6 * 2 = 12 years old. In ten years Ann is going to be 6 + 10 = 16 years old. And Tom is going to be 12 + 10 = 22 years old. So the sum of their ages will be 16 + 22 = 38.
The answer: 38
Reverse engineering the question: Ann is 6 years old. Her brother Tom is now two times older. What will be the sum of their ages 10 years later?

If the first snail traveled the distance in 20 minutes, then the second snail, traveling at twice the rate of speed, would take 20 / 2 = 10 minutes to complete the race. If the third snail raced at five times the speed of the second snail, then it would take the third snail 10 / 5 = 2 minutes to race all the way up the sidewalk.
The answer: 2
Reverse engineering the question: Three snails raced across a rain-soaked sidewalk. The first snail raced at a speed of 2 feet per minute. The second snail raced at twice the speed of the first snail. And the third snail traveled at five times the rate of speed as the second snail. If it took the first snail 20 minutes to race all the way up the sidewalk, how long, in minutes, did it take for the third snail to race all the way up the sidewalk?

On Monday Elisa paints 30 square feet of wall. She paints 2 x 30 square feet on Tuesday = 60 square feet of wall. On Wednesday Elisa paints 1 / 2 as many square feet as she painted on Monday, 1 / 2 x 30 square feet = 15 square feet of wall. In total, Elisa paints 30 + 60 + 15 = 105 square feet of wall.
The answer: 105
Reverse engineering the question: On Monday Elisa paints 30 square feet of her house's walls. On Tuesday she paints twice that amount. On Wednesday she finishes up by painting half as many square feet as she painted on Monday. How many square feet total does Elisa paint in her house?

Anya has 4 x 4 = 16 erasers. Thus, Anya has 16 - 4 = 12 more erasers than Andrea.
The answer: 12
Reverse engineering the question:
Anya has 4 times as many erasers as Andrea. If Andrea has 4 erasers, how many more erasers does Anya have than Andrea?