The school bought 3 skipping ropes, which cost 15 yuan in total. According to this calculation, how much will it cost to buy 15 skipping ropes?
学校买来3根跳绳，一共用去15元．照这样计算，买15根跳绳要用多少元．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">5 * 15</gadget>
<output>75</output>

<result>75</result>