A self-employed person buys 5 tomatoes at 1 yuan, and sells 7 at 2 yuan. If he wants to earn 36 yuan a day, how many tomatoes should he sell every day?
某个体户以1元钱5个的价格购入西红柿，又以2元钱7个的价格卖出，如果他想每天赚36元，那么他每天应卖出多少个西红柿．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(2/7) - (1/5)</gadget>
<output>3/35 = around 0.085714</output>

<gadget id="calculator">36 / (3/35)</gadget>
<output>420</output>

<result>420</result>