Assigning Absolute Configuration to Fischer Projections

 

a
b
c
d
What is the Priority at position a ?
1 2 3 4
What is the Priority at position b ?
1 2 3 4
What is the Priority at position c ?
1 2 3 4
What is the Priority at position d ?
1 2 3 4
What is the Absolute Configuration
R S Achiral