Which line segment is a diameter of circle F?

AC

Step-by-step explanation:

We know that a diameter of a circle is any straight line segment that passes through the center of the circle such that whose endpoints lie on the circle. It is also be known as the longest chord of the circle.

In the given figure we can see that only AC and BE are the  line segments that pass through the center of the circle such that whose endpoints lie on the circle.

18

step-by-step explanation:

draw the shape and you will see that f and k are actually at adjacent vertices (points of the hexagon that are neighboring).   so find the distance between (1,2) and (4,2).   that is easy since (1,2) and (4,2) is just a vertical distance to count, which is 3.   it is a regular polygon which means all sides are congruent.   you have 6 sides (hexa) so multiply 6 by 3 to receive 18.