For the first question:
C.) $240
For the 4 year plan you take $332 a month and multiply by 12 to get the annual value of $3,984. Then multiply that by 4 to get $15,936.
For the 3 year plan take $436×12 to get $5,232, then multiply that by 3 years and you get $15,696.
Finally, to find the difference do $15,936-$15,696 and you get $240.
For the second question:
The new value is between 10 and 12.
Mean refers to the average between all the data paints, while the mean absolute deveiation is the average distance between the data point and the mean. So if the value was 11, for example, the mean, or average would increase from 10, while the MAD would only be 1, decreasing it.