Put simply, it divides two sides of a triangle equally. The midpoint of a side divides the side into two equal segments. As you can see in the picture below, DE is the midsegment of the triangle ABC. Point D divides segment AB into two equal parts, and point E divides segment CB into two equal parts.
You take 143.75 and multiply by .3 to find the amount you will discount from 145.75, to get 102.025. Then multiply that by .095 to get 9.692375. Subtract that from 102.025 to get 92.33.