Explanation

[Solution from source] The C=C bond has two different groups on each carbon, so it shows cis–trans isomerism (2 forms). The CHBr carbon carries H, Br, CH₃ and CH₂CH=CHCH₃, so it is a stereocentre (2 forms). These are independent, giving 2 × 2 = 4 stereoisomers. Counting only one source of isomerism would give 2. Answer (2).