Mineral water in Xinxin supermarket costs 7 yuan for 6 bottles when purchased, and 3 yuan for 2 bottles when sold. If you want to make a profit of 300 yuan, how many bottles of this mineral water need to be sold.
欣欣超市的矿泉水，进货时6瓶7元，售出时2瓶3元，要想获利300元，需售出这样的矿泉水多少瓶．
<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">7 / 6</gadget>
<output>7/6 = around 1.166667</output>

<gadget id="calculator">(3/2) - (7/6)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">300 / (1/3)</gadget>
<output>900</output>

<result>900</result>