The unit price of a commodity is 50 yuan. If it is sold at a price of 60 yuan, the local market will be saturated after 400 units are sold. At the same time, market research shows that for every 2 yuan increase in the unit price of this commodity, its sales volume will decrease by 20 yuan. indivual. In order to earn the most profit, how much should the selling price be?
一种商品进货单价为50元，如果按60元的定价售出，卖出400个后本地市场就将饱和，同时市场调查表明，此种商品单价每涨2元，其销售量就将减少20个．为了能赚取最多的利润，售价应定为多少元？
<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">60 + 15</gadget>
<output>75</output>

<result>75</result>