I am afraid Dott.ssa Russo got all sentences wrong.

The sentences should be done as follows:

How many times has Allan visited London this month?
He has visited it 3 times.

What did your best friend want to tell you on the phone yesterday?
He wanted to tell me about her b'day party.

Have you already invited mark and his wife to dinner?
Yes I did that an hour ago.

When did you buy that cool shirt?
I bought it last saturday.