Write a function named getCostOfCoffee() that has a parameters named numberOfCoffees and pricePerCoffee. Given this information, the function returns the total cost of the coffee order. This is not a simple multiplication of cost and quantity, however, because the coffee shop has an offer where you get one free coffee for every eight coffees you buy.
For example, buying eight coffees for $2.50 each costs $20 (or 8 × 2.5). But buying nine coffees also costs $20, since the first eight makes the ninth coffee free. Buying ten coffees calculates as follows: $20 for the first eight coffees, a free ninth coffee, and $2.50 for the tenth coffee for a total of $22.50.