You can put this solution on YOUR website! Rate is units of trenches per day. Find the rate of 1 man. One man is 1/3 of three men. His rate is therefore of trenches per day. This one-man rate is trench per day.
Now you have rate*time=trenches. For 4 men doing this work, , where is how many days for four men to dig 24 trenches. Find .