Mother spent 1.7 yuan to buy radishes, 0.8 yuan more to buy radishes than to buy cabbage, and 3.9 yuan more to buy eggs than to buy cabbage. How much did my mother spend on eggs?
妈妈买萝卜用去1.7元，买萝卜比买白菜多用0.8元，买鸡蛋比买白菜多用3.9元，请问妈妈买鸡蛋用了多少元？
<gadget id="calculator">1.7 - 0.8</gadget>
<output>0.9</output>

<gadget id="calculator">0.9 + 3.9</gadget>
<output>4.8</output>

<result>4.8</result>