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?
Patrick earned $0.50 x 15 = $<<0.5*15=7.50>>7.50 from selling the lemonade for $0.50 per cup.
So for four hours, his total earnings are $7.50 x 4 = $<<7.5*4=30>>30.
He earned $0.60 x 10 = $<<0.60*10=6>>6 from selling the lemonade for $0.60 per cup.
So for two hours, his total earnings are $6 x 2 = $<<6*2=12>>12.
Therefore, Patrick earn a total of $30 + $12 = $<<30+12=42>>42 from selling lemonade for 6 hours.
#### 42