A, B, C, and D are four barrels of oil, the average of each barrel of A, B, and C is 24 kilograms, and the average of each barrel of B, C, and D is 26 kilograms. It is known that the weight of the D barrel is 28 kg, and how much is the weight of the A barrel.
甲、乙、丙、丁四桶油，甲、乙、丙三桶平均每桶24千克，乙、丙、丁三桶平均每桶26千克．已知丁桶重28千克，甲桶重多少千克．
<gadget id="calculator">24 * 3</gadget>
<output>72</output>

<gadget id="calculator">26 * 3</gadget>
<output>78</output>

<gadget id="calculator">28 - 78</gadget>
<output>-50</output>

<gadget id="calculator">72 + (-50)</gadget>
<output>22</output>

<result>22</result>