It is known that the quotient of the big and small numbers is 4, and the difference between the two numbers is 39, so what is the smaller of the two numbers?
已知大、小两个数的商是4，这两数的差是39，那么这两个数中较小的一个数是多少？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">39 / 3</gadget>
<output>13</output>

<result>13</result>