I think it's 12x.
I'm not a 100% sure though, but I hope this helps. =^D
The answer would have to be
D
You're looking for c, so you want to isolate it or get it by itself. To get rid of the /3 you multiply since the opposite of division is multiplication and to get rid of it, you do the opposite (like -9 you would add 9 to get it to 0). Now you are left with -19+c = 24 (the 24 is 8*3 because what you do to one side you do to the other. Now you get c by itself so you add 19 to both sides which leaves you with C= 43. Sorry if this was confusing!
All exterior angles of n-gon always add up to 360°
To find the number of sides:
