The number A is 15.6, and the number B is 3 times that of A, what is the average of the two numbers?
甲数是15.6，乙数是甲数的3倍，两数的平均数是多少．
<gadget id="calculator">15.6 * 3</gadget>
<output>46.8</output>

<gadget id="calculator">15.6 + 46.8</gadget>
<output>62.4</output>

<gadget id="calculator">62.4 / 2</gadget>
<output>31.2</output>

<result>31.2</result>