how to write a method of Workflow with conditonal loop

i have created one workflow with conditional statement. Example: workflow stages START ,  A ,  B , C , D , END there are six stages. first i am giving condition

(1) if x>=99.99 the workflow will direct stage A to B

(or)

(2) if x>=90 && x<=95.99 the workflow will direct stage A to C 

(or)

(3) if x<=89.99 the workflow will direct stage A to D

 how to write the method for the workflow

Regards,

Krish