Question: For four hours, Patrick sold 15 cups of lemonade per hour at a price of $0.50 per cup.  In the next two hours, he sold 10 cups of lemonade per hour at a price of $0.60 per cup.  How much money did Patrick earn, in dollars, from selling lemonade for 6 hours?
Solve this problem. 
Answer: 
Patrick earned $0.50 x 15 = $7.50 from selling the lemonade for $0.50 per cup.
So for four hours, his total earnings are $7.50 x 4 = $30.
He earned $0.60 x 10 = $6 from selling the lemonade for $0.60 per cup.
So for two hours, his total earnings are $6 x 2 = $12.
Therefore, Patrick earn a total of $30 + $12 = $42 from selling lemonade for 6 hours.