$12.$ In a simple inventory simulation such as the Butler Electric Supply example, which of the following best describes the formula for calculating net profit?

Group of answer choices

net profit $=($selling price X demand$)$

net profit $=($gross profit $$ material costs$)$

net profit $=$ demand $($fixed cost $+$ variable cost$)$

net profit $=$ gross profit $($holding cost $+$ shortage cost$)$