The shopping mall bought a batch of pencil cases at a price of 3.2 yuan each, and the price was 5 yuan each. When there were 80 unsold ones, the profit of the sold ones was 648 yuan. How many pencil cases are there in this batch?
商场以每个3.2元的价格购进了一批文具盒，每个售价5元，还剩下80个没售出时，已售出的获利648元．问这批文具盒一共有多少个．
<gadget id="calculator">5 - 3.2</gadget>
<output>1.8</output>

<gadget id="calculator">648 / 1.8</gadget>
<output>360</output>

<gadget id="calculator">360 + 80</gadget>
<output>440</output>

<result>440</result>