A product is composed of 1 large part and 3 small parts. It is known that the master produces 8 large or 18 small parts per hour, and the apprentice produces 4 large or 12 small parts per hour. If 40 sets of this product are to be produced, how many hours must the master and apprentice work together at least.
一种产品是由1个大零件和3个小零件组成的，已知师傅每小时生产8个大或者18个小零件，徒弟每小时生产4个大或者12个小零件．如果要生产40套这种产品，那么师、徒两人至少需要合作多少小时．
<gadget id="calculator">40 / 8</gadget>
<output>5</output>

<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">12 * 5</gadget>
<output>60</output>

<gadget id="calculator">120 - 60</gadget>
<output>60</output>

<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">60 / 30</gadget>
<output>2</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<result>7</result>