A piece of wood is sawed into sections every 3 meters, sawed 4 times, just finished sawing. How many meters is this wood
一根木头，每3米锯成一段，锯了4次，正好锯完．这根木头多少米
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>