In June the hobby store sold 21,122 + 3,922 = 25,044 trading cards. Over June and July the store sold 25,044 + 21,122 = 46,166 trading cards.
The answer: 46166
Reverse engineering the question: The hobby store normally sells 21,122 trading cards per month. In June, the hobby store sold 3,922 more trading cards than normal. If the hobby store sold the regular number of trading cards in July, how many trading cards did the hobby store sell in June and July combined?

Green = 156 cm. Red = 3 * 156 + 8 = 476 cm. 156 + 476 = 632 cm of yarn. The two pieces of yarn have a length of 632 centimeters.
The answer: 632
Reverse engineering the question: The green piece of yarn is 156 cm long. The red yarn is 8 cm more than three times the length of the green yarn. What is the number of centimeters in the total length for the 2 pieces of yarn?

First figure out how old Ana is right now by subtracting 3 from 15: 15 - 3 = 12. Next, figure out how old Billy is by dividing Ana's age by 2: 12 / 2 = 6. Now figure out how old Mark is by adding 4 to Billy's age: 6 + 4 = 10. Now, to figure out Sarah's age, first multiply Mark's age by 3: 10 * 3 = 30. Finally, subtract 4 from triple Mark's age to find Sarah's age: 30 - 4 = 26.
The answer: 26
Reverse engineering the question: Sarah's age is equal to three times Mark's age minus 4. Mark is four years older than Billy. Billy is half Ana's age. If Ana will be 15 in 3 years, how old is Sarah?

If half of the fruit equals 9 pieces, then Tanya bought 2 * 9 = 18 pieces of fruit. Thus, Tanya bought 18 - 6 - 4 - 2 = 6 plums.
The answer: 6
Reverse engineering the question:
Tanya went to the grocery store to buy some fruit. She bought 6 pears, 4 Granny Smith apples, 2 pineapples, and a small basket of plums, which were all placed in a single paper bag. Unfortunately, the bag that the fruit had been placed in had developed a hole. Therefore, as Tanya walked home, half of the fruit fell out of the bag. When she later counted the fruit left in the bag, there were only 9 pieces remaining. How many plums did she buy?