In a field with 10 ridges side by side, choose 2 ridges to plant two crops A and B, and plant one ridge for each crop. In order to facilitate the growth of crops, it is required that the distance between the two crops A and B is not less than 6 ridges, how many different ridge selection methods are there?
在一块并排10垄的田地中，选择2垄种植A、B两种作物，每种作物种植一垄．为有利于作物生长，要求A、B两种作物的间隔不小于6垄，则不同的选垄种植方法有多少种．
<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>