I believe it is because of weight if Timmy is larger and bigger than Maria that would mean he would stop slower just because of his bodyweight pushing on the back of the skateboard while Maria is all those skinny and she doesn’t have as much weight as she can go farther
Is the velocity constant? Is there any friction?
3 meters per second
then after 40 seconds it must 3*40 = 120 meters
120 meters or 0.12 km if you will
In a stronger gravitational field a given mass will have a larger weight.