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

<result>42</result>