(a)[3]
Anya purchases $4$ shirts and $3$ hats. She hands over $\$100$ and gets $\$21.50$ back as change. Every shirt has the same price. Each hat is priced at $\$13.50$. Find the price of one shirt.
(b)[2]
The dollar–euro exchange rate is $\$1 = €0.91$. Anya buys a new camera for $\$150$. She finds the same camera listed online at €140. Work out the difference between the dollar price and the euro price. Give your answer in dollars, correct to the nearest cent.
(c)[3]
Anya places $\$600$ into a savings account. The account earns compound interest at $r\%$ per year. After $3$ years, the total interest is $\$21.86$. Calculate the value of $r$.