An installment contract for the purchase of a car requires payments of $\$ 260.41$ at the end of each month for 2.25 years. Interest is $5 \%$ per annum compounded monthly. (a) What is the amount financed? (b) How much is the interest cost? (a) The amount financed is $\$$ (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.) (b) The interest is $\$ \square$. (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.)

Step 1 ：Given that the monthly payment (PMT) is $260.41, the annual interest rate (r) is 5% or 0.05, the number of compounding periods per year (n) is 12 (monthly), and the number of years (t) is 2.25.

Step 2 ：We can calculate the amount financed using the formula for the present value of an annuity: \(PV = PMT \times \left[\frac{1 - (1 + \frac{r}{n})^{-nt}}{\frac{r}{n}}\right]\).

Step 3 ：Substituting the given values into the formula, we get \(PV = 260.41 \times \left[\frac{1 - (1 + \frac{0.05}{12})^{-12 \times 2.25}}{\frac{0.05}{12}}\right]\).

Step 4 ：Solving the equation, we find that the amount financed (PV) is approximately $6636.94.

Step 5 ：We can calculate the interest cost by subtracting the amount financed from the total payments made over the 2.25 years. The total payments made is \(PMT \times n \times t = 260.41 \times 12 \times 2.25\).

Step 6 ：Subtracting the amount financed from the total payments, we get the interest cost is approximately $394.13.

Step 7 ：Final Answer: (a) The amount financed is \(\boxed{\$6636.94}\). (b) The interest cost is \(\boxed{\$394.13}\).