HELP ME PLS THIS IS THE LAST THIS I HAVE TO DO AND I CANT FIGURE IT OUT!!! A 40 kg girl is pushing a 40 kg boy in a 20 kg toy wagon.

*The wagon is moving at a constant speed of 2.0 m/s. Calculate the combined kinetic energy of the boy and the wagon.
*They come to a hill going downward, and the girl joins the boy in the wagon, which continues to move at 2.0 m/s at first. Calculate the combined kinetic energy of the two children and the wagon.
*As they travel down the hill, the wagon speeds up to 4.0 m/s. Calculate the kinetic energy of the two children and the wagon after the increase in speed.