1. 2+0.5+2.5= 3. 2km/hr average
2. 14-6=4seconds. 8m/s in 4s = 2m/s acceleration
3. 15m/s divided by 2.5 = 6m/s acceleration
Answer = Matter.
Matter is anything that has mass and takes up space.
______________________________________________
Other solutions may be :
Energy
_______________________________________________
i really hope this helps you a lot , have a nice day : )