−CH3 the number of stereoisomers is given by sum of geometrical isomers (because of presence of C = C)and optical isomers (because of presence of chiral carbon atom). Number of geometrical isomers = 2 (one C = C is present). Number of optical isomers = 2 (one chiral carbon atom). Total number of stereoisomers = 2 + 2 = 4