please help need asap will upvote :)

1. Draw R and S configurations for the following compound. a) (CH3H2C)C(Br)(COOH)(CH3) four different groups in the parenthesis. Draw perspective 3D and Fischer projections. (8 points) b) Assign correct configuration for the following compound ( R or S configuration). (4 points) 1 c) For the following compound identify how many chiral carbons present and how many isomers are possible. (6 points) d) Figure out elements of unsaturation for the following compound (4 points) C6H4NOBr