This is a simple multiplication series. Each number is 3 times greater than the previous number.
Look at this series: 0.7, 2.1, ____, 18.9, 56.7, ... What number should fill the blank?
Options:
[a] 6.3
[b] 5.3
[c] 6.2
[d] 6.1
[e] 4.3