Given time interval [4,15] represents one dimensional unit. we know that one dimensional quantity is graphed on the number line. all the vallues of interval [4,15] is basically the distance which is counted from the origin. [4,15] means lowest possible value of distance is 4 unit from origin while maximum possible value of distance from the origin is 15 unit.
We have to find maximum value so the answer will be 15 units from the origin.
