12 cars form a row and move forward. Counting from the front, the white car is the 8th. Asking how many cars it is from the back.
12辆汽车组成一列向前行进，从前面数起，白色小轿车是第8辆，问从后面数起，它是第多少辆．
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>