Q: A set of 7 spoons costs $21. If each spoon would be sold separately, how much would 5 spoons cost?
A: A set of 7 spoons costs $21, so one spoon from the set costs 21 / 7 = $3. So if sold separately, 5 spoons would cost 5 * 3 = $15. The answer is 15.

Q: In a math contest, Riley and Ofelia are on one team. The team's final score is obtained by adding the scores of the students of the same team. Out of the 35 questions, Riley got 3 mistakes while Ofelia got 5 more than half the score of Riley. How many incorrect answers did their team get?
A: Riley's score is 35 - 3 = 32. Half of Riley's score is 32 / 2 = 16. So Ofelia's score is 16 + 5 = 21. Hence, Ofelia got 35 - 21 = 14 incorrect answers. Therefore, their team got 3 + 14 = 17 incorrect answers. The answer is 17.

Q: Will's breakfast supplied him 900 calories of energy. Then he decided to jog for half an hour, which used up 10 calories of energy per minute. What is Will's net calorie intake after jogging?
A:
Will jogged for 60 / 2 = 30 minutes. He was able to use up 10 x 30 = 300 calories for jogging. The net calorie intake of Will after jogging is 900 - 300 = 600. The answer is 600.