The function for the cost of materials to make a biscuit is f(x) = four-fifths x + 4, where x is the number of biscuits. the function for the selling price of those biscuits is g(f( where g(x) = 4x + 5. find the selling price of 15 biscuits. the answers are: 16 56 65 69

We have two functions.
One determines the cost of the materials, .
The other determines the selling price, .

Now one thing to notice is that in the first function, x is the number of biscuits.
In the second function, however, x is the cost of the materials, as indicated by the price of the biscuits being g(f(x)).

So, let's find the cost of the materials for making 15 biscuits.
Use 15 for x in our function f(x).





Now that we know f(x) (the cost of the materials), we can find g(f(x)).
Use 16 for x in our function g(x).