The price of a 6-pack of toothbrushes is 30 yuan, and the price of a single toothbrush is 7 yuan. The average price of a 6-pack of toothbrushes is how much cheaper each toothbrush is than that of a single toothbrush.
6支装的牙刷价格为30元，单卖1支牙刷价格为7元，6支装的牙刷平均每支比单卖便宜多少元．
<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<gadget id="calculator">7 - 5</gadget>
<output>2</output>

<result>2</result>