There are 18 basketballs and 15 balls in the sports room. I borrowed 9 balls, how many balls are left in the sports room?
体育室里有18个篮球和15个皮球．我借9个皮球，体育室还剩几个皮球？
<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>