10. if you break it down it becomes 10.
40 to 20 is 20
20 to 10 is 10
10 to 40 is 30
40 to 20 is 20
now if you take the difference between those and break those down its
20 to 10 is 10
10 to 30 is 20
30 to 20 is 10
now if you break those down its
10 to 20 is 10
20 to 10 is 10
10 is your final answer
