First, find the total growth over the three months.
The total growth (G) is the sum of the growths in each month:

Using 8 as a common denominator:

The total growth is 17/8.
Second, find the difference between the second and the third month (S).
To find it, subtract the growth of the second month from the growth of the third month.

Using 8 as a common denominator:

The difference between the second and third months is 3/8.
Answer:
(a) The total growth is 17/8.
(b) The difference between the second and third months is 3/8.