We use the formula to find the vertex of the function. A quadratic function of the form of and equating this form to the given function , we have and .
Substituting and into the vertex formula, we have , as shown in the graph
This calculation means that the highest profit is achieved when the number of photo printed equals to ten photos
Part B:
We can find solution to this equation by factorising
and , as shown in the graph
The two values means that the company makes no profit when they either produce 5 or 15 photos