Xiao Ming bought a ball for 7.9 yuan and bought a pair of table tennis rackets for 17.5 yuan. He gave the salesperson 30 yuan. How much should he get back?
小明买一个皮球用去7.9元，买一副乒乓球拍用去17.5元，他给售货员30元，应找回多少钱？
<gadget id="calculator">17.5 + 7.9</gadget>
<output>25.4</output>

<gadget id="calculator">30 - 25.4</gadget>
<output>4.6</output>

<result>4.6</result>