Final answer:
The total cost function c(x) for installing a new field is obtained by adding the fencing and grass laying cost functions f(x) and g(x). After simplifying, the total cost function is c(x)=25x+900. Option number d is correct.
Step-by-step explanation:
The question is asking for the function c(x) that models the total cost, in dollars, to lay new grass and fence in a rectangular field with an area of x square meters. To find the total cost, you need to add the costs of fencing and laying new grass together.
The cost to fence in the field is modeled by the function f(x)=5x+300, and the cost to lay new grass is modeled by the function g(x)=20x+600. By adding these two functions together, we get:
c(x) = f(x) + g(x) = (5x + 300) + (20x + 600)
Simplifying the right side, we combine like terms:
c(x) = 5x + 20x + 300 + 600 = 25x + 900
Therefore, the function that models the total cost is c(x)=25x+900.