Jimmy got a sum of money from his work-study program in the library during the holidays, and he planned to use the money to buy a book for each student in the class. If you buy all of "The Self-Report of Mars" with a unit price of 11 yuan, you will have 150 yuan left; if you buy all of the "I am an Astronaut" with a unit price of 15 yuan, you will only have 30 yuan left. How many students are there in Jimmy's class?
吉米假期在图书馆勤工俭学获得一笔钱，他打算用这一笔钱为全班同学每人买一本书．如果全部购买单价11元的《火星的自述》，就余150元；如果全部购买单价为15元的《我是宇航员》，就只余30元．吉米班有多少名同学？
<gadget id="calculator">150 - 30</gadget>
<output>120</output>

<gadget id="calculator">15 - 11</gadget>
<output>4</output>

<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<result>30</result>