It takes 3 small sticks to place a triangle, 5 sticks to place two triangles, and how many sticks to place 9 triangles.
摆一个三角形用3根小棒，摆两个三角形是5根，摆9个三角形要多少根小棒．
<gadget id="calculator">2 * 9</gadget>
<output>18</output>

<gadget id="calculator">18 + 1</gadget>
<output>19</output>

<result>19</result>