Q: Brenda is a vet who needs to spay some cats and twice as many dogs. If she needs to spay 21 animals total today, how many cats does she need to spay?
A: Let c be the number of cats Brenda needs to spay and d be the number of dogs. We know that c + d = 21 and d = 2c. Substituting the second equation into the first, we get c + 2c = 21. Combining like terms, we get 3c = 21. Dividing both sides by 3, we get c = 7. The answer is 7.

Q: Every time Carl earned $0.50 he would go to the corner market and buy a candy bar. Carl's neighbor said he would pay him $0.75 every week for taking out his trash. At the end of four weeks, how many candy bars will Carl be able to buy?
A: He is paid $0.75 every week for 4 weeks, so Carl made .75 * 4 = $3.00 in 4 weeks. Each candy bar cost $0.50 and he made $3.00 so 3.00 / .50 = 6 candy bars. The answer is 6.

Q: Jack will have ten times more handball trophies than Michael has right now in three years. If Michael has 30 trophies right now, and the number of his trophies increases by 100 in three years, what's the total number of trophies they'll have altogether after three years?
A:
In three years, Michael will have 30 + 100 = 130 trophies. If Michael has 30 trophies now, Jack will have 10 * 30 = 300 in three years. Altogether, Jack and Michael will have 300 + 130 = 430 handball trophies in three years. The answer is 430.