Beginning in the spring semester of 2008, the state provided free textbooks to rural students in the compulsory education stage. How much should a primary school student pay each semester?
从2008年春季学期开始，国家为农村义务教育阶段学生免费提供教科书，每名小学生每学期只交15元的作业本费，比免费提供教科书以前少交(4/5)，免费提供教科书以前每名小学生每学期应该交多少元？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 / (1/5)</gadget>
<output>75</output>

<result>75</result>