Perform four arithmetic operations on the four numbers 3, 4, 5, and 7, and use each number only once to make the result equal to 24.
3、4、5、7这四个数字进行四则运算，每个数只用一次，使其结果等于24．
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<result>24</result>