A trapezoidal green space made of flowerpots. There are 8 pots on the top, 12 pots on the bottom, and 5 rows. It costs 15 yuan per pot to buy this kind of flowers. How much does it cost to buy these flowers?
一个由花盆摆成的梯形绿地，上底摆了8盆，下底摆了12盆，摆了5排，买这种花每盆要15元，买这些花共要多少元？
<gadget id="calculator">8 + 9 + 10 + 11 + 12</gadget>
<output>50</output>

<gadget id="calculator">15 * 50</gadget>
<output>750</output>

<result>750</result>