Describe how feedback inhibition works

Say you have a pathway 
A-->B-->C-->D 

So your A leads to production of B which leads to production of C which leads to production of D 
In feedback inhibition (or a negative feedback loop), the final product of a pathway (in this case, D) will usually inhibit or stop the first step in that pathway. So in this instance, D would do something to stop A-->B from occurring. It could bind A or the enzyme that makes that step occur. 
Basically, the end product somehow stops one of the earliest steps in the pathway

$100. 125 x 0.20 = 25125 - 25 = $100