Answer:
see attached 0 ⇒ 0–6
Explanation:
Given a table of ages and weights, you want the average rate of change (per month) for consecutive pairs of table values.
Rate of change
The average rate of change is the change in weight divided by the change in age. For example, in the interval 0–6 months, it is ...
(17.4 -7.8)/(6 -0) = 9.6/6 = 1.6 . . . . . pounds per month
The calculations are conveniently done for the rest of the table by a spreadsheet. The results are attached. The value on each line is the average over the interval from that age to the next.