Final answer:
The function g(x) represents the total cost of your friend's pizzas, and it can be written as g(x) = 12x + 48.
Step-by-step explanation:
The function g(x) represents the total cost of your friend's pizzas. Since your friend plans to buy 4 more pizzas than you, the function g(x) can be written as g(x) = f(x+4), where f(x) is the total cost of your pizzas. To simplify this, substitute f(x) with 12x. So, g(x) = 12(x+4), which simplifies to g(x) = 12x + 48.