Option A - am used to doing
Many people often get confused about the use of "used to" and "get used" because they look simila but they are completely different. We use 'used to' to talk about actions that happened in the past that no longer happen now.
Example of this is the sentence in the question above. "When I started to work here I needed a lot of help, but now I am used to doing all the work on my own".
Get used to is used to express an action that becomes less strange. It shows that something is in the process of becoming normal.
If you are used to something, you are accustomed to it – you don’t find it unusual. If you get used to something or you are getting used to something you are becoming accustomed to it – it was strange, now it’s not so strange.