How many stereoisomers of (S)-adenosylmethionine are theoretically possible?

How many stereoisomers of (S)-adenosylmethionine are theoretically possible? Enter your response as the integernumber.

The higher PKa value corresponds to the { STRONGER / weaker } acid.
State which one is right.

Calculate the degree of unsaturation
number of missing H2 units relative to an alkane
for the Compound with the molecular formula
C 16 H13 N2 O CI
Enter your response as an integer number

Give the systematic name for the alkene you should use to prepare 2-bromo-3-methylbutane as the only product upon electrophilic addition of H Br.