A certain supermarket held a May Day event, offering a 20% discount. Xiaogang bought a pencil case and saved 3.6 yuan. How much is the original price of the pencil case?
某超市五一搞活动，一律八折优惠，小刚买了一个文具盒，省了3.6元，文具盒原价多少元？
<gadget id="calculator">80 / 100</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">3.6 / (1/5)</gadget>
<output>18</output>

<result>18</result>