Answer:
D
Explanation:
The formula we need to solve this is:

Where
is the distance from one focus to the vertex
is the second distance from another focus to same vertex
Note: Here, vertex point is the point on top. The common point from which the RED and BLUE line meets the 2 foci
is half the length of the major axis (which is 9 here since total major axis is given as 18)
Now we can plug into the equation and solve:

D is the correct answer.