I can find the finite differences, but how do I find the number of birds in July?

Question

owl.bcpnet. net/Algebra%202/ch6/section09/problem_solving.pdf

Answer 1

Question 3 requires the polynomial model, say P(x) where x is the month, 1 for January, 2 for February, and so
P(7) is the value for July.

So if you have already found the polynomial for question 3, it is a question of substituting the proper month (July) to find P(July) as the number of birds in July.

Answer 2

In case you have difficulties also with Q3, there is a good article that show you how to solve a similar problem step-by-step:
http://www.trans4mind.com/personal_development/mathematics/series/polynomialEquationDifferences.htm