The ratio of a ratio is (7/8). If 21 is added to the preceding term, how much should be added to the latter term to keep the ratio unchanged?
一个比的比值是(7/8)，如果把它的前项加上21，要使比值不变，后项应该加上多少
<gadget id="calculator">7 + 21</gadget>
<output>28</output>

<gadget id="calculator">28 / 7</gadget>
<output>4</output>

<gadget id="calculator">8 * 4</gadget>
<output>32</output>

<gadget id="calculator">32 - 8</gadget>
<output>24</output>

<result>24</result>