The construction site needs 47 tons of cement. First, it was transported 4 times by 2 trucks with a load of 2.5 tons. Later, it was changed to 3 large trucks with a load of 4.5 tons. How many times will it take to complete the task? (solution by equation)
建筑工地需用47吨水泥，先用2辆载重2.5吨的汽车运了4次，后来改用载重4.5吨的大卡车3辆，还需要多少次才能完成任务？(用方程解)
<gadget id="calculator">2.5 * 4 * 2</gadget>
<output>20</output>

<gadget id="calculator">47 - 20</gadget>
<output>27</output>

<gadget id="calculator">4.5 * 3</gadget>
<output>13.5</output>

<gadget id="calculator">27 / 13.5</gadget>
<output>2</output>

<result>2</result>