A class takes (2/3) hours, the teacher spends (1/5) hour explaining, the students use (1/4) hour for the experiment, and the rest of the time is for the students to do their homework. How much time did you spend doing your homework?
一节课需用时(2/3)小时，老师讲解用了(1/5)小时，学生操作实验用了(1/4)小时，其余的时间是学生自己做作业．做作业用了多少时间？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/3) - (1/5) - (1/4)</gadget>
<output>13/60 = around 0.216667</output>

<result>13/60 = around 0.216667</result>