A certain factory has three workshops, the number of people in the first workshop accounts for (1/4) of the total number of people in the three workshops, the number of people in the second workshop is (7/8) the number of people in the third workshop, and the number of people in the first workshop is 21 less than that of the third workshop ． How many people are there in the three workshops?
某工厂有三个车间，第一车间的人数占三个车间总人数的(1/4)，第二车间人数是第三车间人数的(7/8)，第一车间比第三车间少21人．三个车间共有多少人？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">(3/4) * (8/15)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">21 / (3/20)</gadget>
<output>140</output>

<result>140</result>