The price of the basketball is 15 yuan more expensive than the small ball, and the price of the basketball is 4 times that of the small ball. What is the price of the small ball?
篮球的价格比小皮球贵15元，篮球的价格是小皮球的4倍，小皮球的价格是多少元．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>