(a) A linear model for the population P(t) after t weeks have passed is:
P(t) = at + b
where b is the initial population. In this case, b = 32.
Since for t = 10, P(t) = 38, we have:
38 = a * 10 + 32
38 - 32 = 10a
6 = 10a
6/10 = a
a = 0.6
Therefore, the linear model is:
P(t) = 0.6t + 32
(b) Now, after 13 weeks, we have:
P(13) = 0.6 * 13 + 32 = 7.8 + 32 = 39.8
Therefore, after 13 weeks, approximately 40 beetles are expected.
(c) Now, we need to find t for which P(t) = 85:
85 = 0.6t + 32
85 - 32 = 0.6t
53 = 0.6t
t = 53/0.6
t ≅ 88.333
t ≅ 88
Therefore, rounding the result to the nearest week, the answer is:
After 88 weeks.