Final answer:
A linear model that describes the number of dolls Abigail collects over the years is D = 2(A - 5) + 12. Abigail will have 32 dolls at age 15. She will be 19 years old when her collection reaches 40 dolls.
Step-by-step explanation:
To create a linear model representing Abigail's collection of rare dolls, we start with the given information that she has 12 dolls at age 5 and receives an additional 2 dolls every year after her 6th birthday. The linear model can be expressed as D = 2(A - 5) + 12, where D represents the number of dolls, and A is Abigail's age. To find out how many dolls Abigail will have by the age of 15, we substitute A with 15 in the equation: D = 2(15 - 5) + 12 = 2(10) + 12 = 20 + 12 = 32. Therefore, Abigail will have 32 dolls by the age of 15.
Now, to determine at what age Abigail will have a total of 40 dolls, we solve the equation for A. This gives us 40 = 2(A - 5) + 12. Simplifying, we get: 40 - 12 = 2(A - 5), 28 = 2A - 10, 38 = 2A, and therefore A = 38 / 2 = 19. Abigail will be 19 years old when she has 40 dolls.