The number of A is 3 times of the number of B. The sum of the numbers of A and B is 15.6. What is the number of A?
甲数是乙数的3倍，甲、乙两数和是15.6，甲数是多少？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">15.6 / 4</gadget>
<output>3.9</output>

<gadget id="calculator">15.6 - 3.9</gadget>
<output>11.7</output>

<result>11.7</result>