The line for the graph x=1 is the line of reflection that reflects triangle ABC onto triangle A'B'C'.
You have to find the middle points between each pair of identical points and then join them.
Now, a whole, will be 15/15 or 1 whole.
now, the sprinkler does 1/15 of the lawn in 1/3 of an hour, how long will it be to do the whole 15/15?