Answer:
A. c = kn
Explanation:
The cost c varies directly as the numbers n of pencils
This means that c is a multiplication of a constant by n, which is the number of pencils. So the equation for the cost is given by:
![c = kn](https://img.qammunity.org/2022/formulas/mathematics/college/rv7rae4mgypsrvwx47fb42fnwyu2j7vwd6.png)
In which k is the constant of proportionality, that is, the cost of each pencil. So the correct answer is given by option A.