There are 45 basketballs and volleyballs in the sporting goods store, of which basketballs account for 60%. After a batch of basketballs are sold, basketballs account for 25% of the total number. How many basketballs are sold?
体育用品商店有篮球和排球共45个，其中篮球占60%，当卖出一批篮球后，篮球占现存总数的25%，卖出的篮球是多少个？
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">45 * (3/5)</gadget>
<output>27</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">45 * (1/4)</gadget>
<output>45/4 = around 11.25</output>

<gadget id="calculator">27 - (45/4)</gadget>
<output>63/4 = around 15.75</output>

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

<gadget id="calculator">(63/4) / (3/4)</gadget>
<output>21</output>

<result>21</result>