Which number sentence can be used to determine n, the 9th number in the pattern

Answer would be D
Because the pattern is going by 3s and it is asking for the 9th so u just multiply 9 by 3 which give you 27 and if you want to check you answer then subtract 6 by 3 gives you 3 and theater number in the pattern is 15 so you just add 15 by 3 which is 18 and repeat the same thing until you get to the 9th number
18, 21, 24, 27...

40 because it’s just a little longer than 32 feet