There are direct air lines between the four cities. How many air lines are there in total?
在4个城市之间，都有直达的航空线，一共有多少条航空线？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<result>12</result>