Skip counting

This task is about skip counting.
a)
 
Fill in the boxes along the track below by adding the number 2 each time.
 
diagram for skip counting starting at 2, then 4
 
b)
Fill in the boxes below by adding the number 10 each time.
 
diagram for skip counting starting at 200
 
c)
Fill in the boxes below by adding the number 20 each time.
 
diagram for skip counting starting at 400