Question

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(x)), where g(x) = 4x + 5. Find the selling price of 15 biscuits. please help the answers are: 16 56 65 69

Answer 1

We have two functions.
One determines the cost of the materials,
`f(x)=\frac{4}5x+4`.
The other determines the selling price,
`g(x)=4x+5`.

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).


`f(15)=\frac{4}5*15+4`

`f(15)=12+4`

`f(15)=16`

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).


`g(17)=4*16+5`

`g(17)=64+5`

`\boxed{g(17)=69}`