A student asked Mr. Wang how much you just bought Mo Yan's famous literary work "Life and Death Fatigue". Mr. Wang said: "Add 5 to the price of each book, subtract 4, multiply by 5, and divide by 4 is 50." (unit: yuan)". So, how much is the price of each book?
有学生问王老师，您刚买莫言的文学名著《生死疲劳》每本多少元，王老师说："该书每本售价加上5，减去4，乘以5，除以4是50(单位：元)"．那么，该书每本售价多少元．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">50 * (4/5)</gadget>
<output>40</output>

<gadget id="calculator">4 - 5</gadget>
<output>-1</output>

<gadget id="calculator">40 + (-1)</gadget>
<output>39</output>

<result>39</result>