Business calculus is necessary when calculating optimum production quantities which will result in the greatest profit. It is also used to calculate the profit on additional items made (marginal profit). Another use is in determining ideal packaging and shipment sizes. There are many other uses.
The basic idea is this: economists or mathematicians can provide equations for calculating revenues, costs and profits. A curve can be drawn from such an equation. Most of the time, the curve goes up then starts to come down because there is a production quantity above which new costs are higher than new revenues eg. an Apple Store has limited capacity and customers at each location, so we have to determine how many iPhones to ship to the store. Above that number, storage or inventory holding costs begin to eat into our profit on new phone sales. On a graph, the ideal quantity occurs at a maximum y-value, where the curve turns and starts going down. Calculus is a convenient way to calculate the x and y-values at a turning point on any curve.
If you are not familiar with calculus, it is simply a technique for measuring slopes on a curve and the area under a curve.
Only 10% of student difficulty with calculus stems from the complexity of the subject. 90% of difficulty stems from weak basics in Algebra and PreCalc. These can be quickly remedied or patiently explained as you learn calculus itself.