(a) 6 (b) 8 ( c) 1 0 (d) 16
It has 4 chiral centres which are marked with asterisk.
Number of stereoisomers = 2^4 = 16
This 16 number includes enantiomers , diastereomers and meso forms.Out of 16 six are meso forms which are optically inactive due to plane of symmmetry.
check attached file
Second image is of one of the meso form