How do you calculate the magnitude of the resultant force of two forces acting on an object in the same direction?

Anybody wanna ? (picture included? )

Mutt and jeff are running along a path each pushing a cart loaded with rocks. if mutt's wagon has a mass two times greater than jeff's and they want to stay together, arriving at their destination at the same time, what must happen? a) jeff should slow down so mutt can catch up. b) mutt must use half as much force to push his cart. c) mutt must use twice as much force to push his cart. d) mutt and jeff will use the same force, but mutt will take bigger steps.

Suppose a comet has an orbital period of 309.1 years around the sun. what is it’s average distance from the sun?