If the middle term of a proportion is 8 and the first term of the proportion is 5, what is the fourth term of the proportion?
一个比例的比例中项为8，比例的第一项为5，则第四比例项为多少．
<gadget id="calculator">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">64 / 5</gadget>
<output>64/5 = around 12.8</output>

<result>64/5 = around 12.8</result>