The correct answer is D.41.
1. Since is the midpoint of , we know that (by the definition of a midpoint, which divides a line segment into two equal parts). That is, .
Given that and , we can set up the equation:
.
2. Expand the left side of the equation:
Using the distributive property , where , , and , we get .
3. Solve for :
Subtract from both sides of the equation: