There's really no way to calculate Molly's pulling force, because all
of the data given in the question only describes Samantha's situation.
The following solution assumes that Molly's wagon and dog are identical
in mass, acceleration, and frictionlessness to Samantha's:
Force = (mass) x (acceleration) =
(45 kg) x (0.85 m/s²) = 38.25 newtons
(Assuming there's no friction anywhere in the wagon/ground system.)
