1. **State the problem:** Calculate the total cost using instalment plan and compare with after-tax cash price for furniture, then analyze the cost and payments for a used car. \n 2. **Calculate total cost for sofa and love seat using instalment plan:** Let the monthly instalment be $P$ and the number of months $n$. Since the HST is included in instalments, total cost is simply $P \times n$ plus down payment if any. \n 3. **Recall after-tax cash price for furniture from #1:** Suppose cash price before tax is $C$, tax rate is $t$, after-tax price is $C (1 + t)$. \n 4. **Calculate difference:** Difference $= \text{Total instalment cost} - \text{After-tax cash price}$ This represents the interest paid on the loan. \n 5. **Calculate after-tax cash price of the car:** Cash price $= 3999$ Assuming HST = 13% = 0.13, After-tax price $= 3999 \times (1 + 0.13) = 3999 \times 1.13 = 4518.87$ \n 6. **Calculate how many monthly payments to pay loan in full:** Down payment $= 1000$ Monthly payment $= 199$ Loan balance after down payment $= 4518.87 - 1000 = 3518.87$ Number of payments needed $= \lceil \frac{3518.87}{199} \rceil = \lceil 17.68 \rceil = 18$ months \n 7. **Calculate total cost of monthly payments:** Total monthly payments $= 199 \times 18 = 3582$ **Final answers:** - After-tax cash price of car: $4518.87$ - Number of monthly payments: 18 - Total cost of monthly payments: $3582$ Note: The problem's furniture prices and instalment amounts are not specified; these steps guide you how to calculate given data.