There is a set of (1, 3), (2, 6), (3, 9), (4, 12), ..., what is the sum of the sixth set of numbers.
有一数组(1，3)、(2，6)、(3，9)、(4，12)、…，第6组数的和是多少．
<gadget id="calculator">6 + 18</gadget>
<output>24</output>

<result>24</result>