Reduce -8 + b^2 by 5 + b^2. -3
-13
2b² - 3

i know the answer is -13 but can you please explain as simply as you can how you got that? Cause i don't get it.

-13 is the answer

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.