The young pioneers of the four classes of the fourth grade of the Experimental Primary School donated to the "Hope Project". The average donation of the first, second and third classes was 240 yuan per class; , How much is the contribution of the fourth class?
实验小学四年级四个班的少先队员为"希望工程"捐款，一、二、三班平均每班捐款240元，二、三、四班平均每班捐款260元，已知一班捐款220元，四班捐款多少元？
<gadget id="calculator">260 * 3</gadget>
<output>780</output>

<gadget id="calculator">240 * 3</gadget>
<output>720</output>

<gadget id="calculator">720 - 220</gadget>
<output>500</output>

<gadget id="calculator">780 - 500</gadget>
<output>280</output>

<result>280</result>