Final answer:
The cost of a car is £8700 when the monthly payment is £400 and the deposit is £1500. The monthly payment is £250 when the deposit is £3000 and the cost of the car is £7500.
Step-by-step explanation:
To find the cost of a car when the monthly payment is £400 and the deposit is £1500, we can plug these values into the given formula: cost = 18 × monthly payment + deposit. So, cost = 18 × £400 + £1500 = £7200 + £1500 = £8700.
To find the monthly payment when the deposit is £3000 and the cost of the car is £7500, we can rearrange the formula to solve for the monthly payment: cost = 18 × monthly payment + deposit. Rearranging the formula gives: monthly payment = (cost - deposit) / 18. Substituting the given values, we get: monthly payment = (£7500 - £3000) / 18 = £4500 / 18 = £250.