The weight of 1 apple and 1 banana is the weight of 7 iron nuggets, and the weight of 1 apple is the weight of 4 iron nuggets. How many iron nuggets weighs the weight of 1 banana?
1个苹果和1个香蕉的重量是7个小铁块的重量，而1个苹果的重量是4个小铁块的重量，1个香蕉的重量是多少个小铁块的重量？
<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<result>3</result>