Choose the segment with the error. If there is no error, choose option 4.
Your account should/1 have been credited/2 with three months' interest./3
For a "no error" type question, the safest method is to look for one common mistake type in each segment: wrong tense, wrong voice, wrong preposition, or wrong possessive form.
None of the three segments show a tense, voice, preposition, or possessive mistake, so the sentence as printed is fully correct.
Let's summarize:
So option 4 (no error) is the answer.
Identify the part of the sentence that contains an error:
"Neither the manager nor the employees ___ willing to accept the new policy."