An 80 cm long wooden strip needs to be sawed into small pieces of 4 cm each. It takes 3 minutes to saw each time (sawing can not be overlapped). How many minutes will it take to finish sawing.
一根80厘米长的木条，要锯成每段是4厘米的小段，每锯一次需要3分钟(锯的时候不能重叠)，一共要用多少分钟锯完．
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">19 * 3</gadget>
<output>57</output>

<result>57</result>