M = (1,4)
N = (5,2)
For M, you simply move to 1 on the x axis abs for 4 you move on the y axis. Same does for N, for 5 you move on the x axis and for 2 you move on the y axis.
You do 3/5 minus 3/5 which cancels out to 0. Then you do 6 minus 4 which is 2. The answer is 2.
CAC can be changed into CAAC. This is because the first rule says that any letter can change into an A so
CAC=CAA
The last condition says that when you double , you have to double all letters,
Since A has been doubled,C needs to be doubled too.So:
CAA=CAAC