A computer operating company bought back a batch of computers, sold (1/4) in the first week, and sold 21 units in the second week. At this time, the ratio of the number of remaining units to the number of units sold was 2:3. This batch of computers How many original sets?
某电脑经营公司购回一批电脑，第一个星期卖出(1/4)，第二个星期卖出21台，这时余下的台数与卖出的台数比是2：3，这批电脑原有多少台？
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/5) - (1/4)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">21 / (7/20)</gadget>
<output>60</output>

<result>60</result>