There used to be 20 yuan in the piggy bank. Yesterday I bought a pen with 7.8 yuan, and today my mother gave me another 4.6 yuan. How much money is in the piggy bank now?
存钱罐里原来有20元钱，昨天我用7.8元买了一支钢笔，今天妈妈又给了我4.6元．存钱罐里现在有多少钱？
<gadget id="calculator">20 - 7.8</gadget>
<output>12.2</output>

<gadget id="calculator">12.2 + 4.6</gadget>
<output>16.8</output>

<result>16.8</result>