A street vendor buys three mangoes for 10 yuan and sells them for 21 yuan for 5 mangoes. If he wants to make a profit of 130 yuan, how many mangoes does he need to sell?
街边小贩以10元钱3个的价格买进芒果若干个，又以21元钱5个芒果的价格卖出．如果他要赚得130元钱的利润，那么他需卖出芒果多少个？
<gadget id="calculator">21 / 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">10 / 3</gadget>
<output>10/3 = around 3.333333</output>

<gadget id="calculator">(21/5) - (10/3)</gadget>
<output>13/15 = around 0.866667</output>

<gadget id="calculator">130 / (13/15)</gadget>
<output>150</output>

<result>150</result>