The series is formed by multiplying the previous term by sequentially decreasing decimal values and adding a sequential integer. Multiplying 8 by 0.5 and adding 2 gives 6, multiplying 6 by 1 and adding 4 gives 10, and multiplying 10 by 1.5 and adding 6 gives 21. Continuing this pattern, multiplying 21 by 2 and adding 8 gives 50, and multiplying 50 by 2.5 and adding 10 gives 135. The missing term is 135.