"Identify the context" means write down, for each step, a member of E that enabled the step according to the definition of |->v. Example:

    (+ 1 (+ 2 (+ 4 5)))
    |->v     E = (+ 1 (+ 2 []))
    (+ 1 (+ 2 9))
    ...

This exercise 6.1 will count as 0.5 bonus points for the homework if you received no credit for 6.1 in the previous homework.