Zhang Lijun and Liu Dawei in my class want to buy a football together. Zhang Lijun has 13.2 yuan, and Liu Dawei has 16.8 yuan. The price of a football is twice the sum of their money. How much money do they have to buy a football?
我班的张利军和刘大伟俩要合买一个足球．张利军有13.2元，刘大伟有16.8元，一个足球的价钱是两人钱数总和的2倍，他们要买一个足球还差多少元
<gadget id="calculator">13.2 + 16.8</gadget>
<output>30</output>

<result>30</result>