Find the 29th term of the following sequence.
21, 15, 9, 3, . . .
To find the 29th term of the sequence, we need to determine the pattern. We start with 21 and then subtract 6 to get the next term 15. Then we subtract 6 again to get the next term 9. The pattern continues by subtracting 6 each time. Therefore, to find the 29th term, we subtract 6 a total of $29-1=28$ times.
Starting with 21, we subtract 6 a total of 28 times: $$21-6(28) = 21 - 168 = \boxed{-147}.$$