4 , 2 , ?, 7.5, 26.25, 118.125

As per the details in the question the series is in the form of
First term = 4
Second term = First term × 0.5
? Second term = 4 × 0.5 = 2
Third term = Second term × 1.5
? Third term = 2 × 1.5 = ?
? ? = 3
Fourth term = Third term × 2.5
? Fourth term = 3 × 2.5 = 7.5 ;
Fifth term = Fourth term × 3.5
? Fifth term = 7.5 × 3.5 = 26.25 ;
Similarly , we can find all others terms also.
Sixth term = Fifth term × 4.5
? Sixth term = 26.25 × 4.5 = 118.125;
Hence , Third term = 3