The definition of work is that it is the Force applied over a distance, times the distance. The only trick is that you have to account only for forces in the direction of movement; any forces that are normal to the movement are not taken into account. Intuitively, work is generated only by forces that contribute to the movement (or go against it; same or opposite direction).
Let us see now: W=F*d =11.2N* 15.9m=178.1 N*m=178.1 J where J stands for Joules. This is the work that the parent did, namely how much energy he had to put in to move the stroller.
