This problem is an inverse proportion case. Having two variables: number of workers and time (in days); when we increase the number of workers, the time needed decreases; vice versa. Therefore, we can use the multiplication method: (workers * time) will always stay constant.
Let's say the time (in days) needed by the eleven workers is t,
5*20 = (3*10) + (14*t)
100 = 30+14t
70 = 14t
5 = t
It will take the eleven-workers 5 more days to finish the road.
