Lan Lan participated in the summer camp, and originally planned to pay 135 yuan for accommodation for 9 days, but the summer camp was extended by 4 days. How much does Lan Lan have to pay?
兰兰参加夏令营，原计划9天交135元住宿费，后来夏令营延长了4天．兰兰还要补交多少钱？
<gadget id="calculator">135 / 9</gadget>
<output>15</output>

<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<result>60</result>