Final answer:
The expected U.S. population in 2010, according to the given model, is approximately 296 million.
Step-by-step explanation:
To find the expected U.S. population in 2010 according to the given model, we need to substitute the value of x = 20 into the function P(x). The model is given as P(x) = 250,000,000e^(0.009x), where x is the number of years after 1990. Therefore, P(20) = 250,000,000e^(0.009*20).
Using a calculator to evaluate the right side of the equation, we get P(20) ≈ 295.9234 million. Rounding to the nearest million, the expected U.S. population in 2010 according to this model is approximately 296 million (option b).