Final Answer:
Dan can afford a car worth approximately $18,112.14, considering a monthly payment of $400, a prevailing interest rate of 4.4% per year compounded monthly for a 48-month loan, and a $6,000 trade-in.
Step-by-step explanation:
Dan's affordability for a new car can be determined using the formula for the monthly payment of a loan:

where PMT is the monthly payment, P is the loan amount, r is the monthly interest rate, and n is the number of payments. In Dan's case, PMT = $400),
= 0.00367 (monthly interest rate), and n = 48 months.
Rearranging the formula to solve for (P):

Substituting the given values:
P = \dfrac{$400 \cdot ((1 + 0.00367)^{48} - 1)}{0.00367 \cdot (1 + 0.00367)^{48}} \approx $18,112.14.
This calculation indicates that Dan can afford a car worth around $18,112.14. To find the total amount he can spend, we add the trade-in value of $6,000. Therefore, the most expensive car Dan can afford is approximately $18,112.14 + $6,000 = $24,112.14.