What are the steps to solve an optimization problem?

I - Extract or state the function to be maximized or minimized from the problem conditions.
II - If the problem involves more than one variable, set up equations that relate the different variables of the system.
III - Solve the equation and substitute it into the function so that we have a function with a single variable.
IV - Find the local extremes by setting the function to zero and solving the resulting equation.
a) I and II are correct.
b) I, II, and III are correct.
c) II and IV are correct.
d) I, III, and IV are correct.