It takes 100,000 years for a plate to move about 2 kilometers. what's the rate of motion in centimeters per year? ?

2km is the same as 2000m which is the same as 200000 cm.
BUT don't make the same mistake as the other answer. This is 200000 cm per 100000 years. Divide 200000 by 100000 to get 2 cm per year.
Hope this helps!

Answeroil-shale;