Dad went to the fruit shop to buy fruit and paid a total of 41.9 yuan. He first bought 2.5 kilograms of apples at 7.8 yuan per kilogram, and then bought 3.5 kilograms of oranges with the remaining money. How much is the orange per kilogram? (solution with equation)
爸爸到水果店买水果，一共付了41.9元，先买了每千克7.8元的苹果2.5千克，余下的钱买了3.5千克橘子，橘子每千克多少元？(用方程解答)
<gadget id="calculator">7.8 * 2.5</gadget>
<output>19.5</output>

<gadget id="calculator">41.9 - 19.5</gadget>
<output>22.4</output>

<gadget id="calculator">22.4 / 3.5</gadget>
<output>6.4</output>

<result>6.4</result>