In class, students spend (1/5) hours doing experiments, teachers use (3/10) hours to explain, and the rest of the time students do homework independently. It is known that each class is 40 minutes, how much time did the students spend doing homework?
课堂上学生做实验用(1/5)小时，老师讲解用(3/10)小时，其余的时间学生独立做作业．已知每堂课是40分钟，学生做作业用了多少时间？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<result>10</result>