11. I am was not very (SUCCESS) as an accountant, his colleagues often had to help him.

Solution:

The sentence indicates a lack of success in a particular role. The word 'SUCCESS' needs to be converted into an adjective describing the state of not being successful. This is 'successful', and the negation would be 'unsuccessful' or, as indicated by the following phrase, 'not very successful'. The structure requires the adjective form.

Answer: 11. I was not very successful as an accountant.