It is known that each pair of table tennis rackets is a yuan. Teacher Liu bought 4 pairs and paid 100 yuan to the salesperson. Use the formula to express the amount of money that the salesperson gave Teacher Liu.
已知乒乓球拍每副a元，刘老师买了4副，付给营业员100元，用式子表示营业员找给刘老师的钱数．
<gadget id="calculator">100 - 4</gadget>
<output>96</output>

<result>96</result>