Please help with this homework?

Mr. ..., the man who runs the corner shop, phoned at 9:30 a.m. about his company's new computer system, which you installed. [This might run smoother if you said "the new computer system you installed for his company."] Apparently, there's something not quite right with it, and he needs your advice. He's asked that you phone him back sometime today or tomorrow (preferably today, if possible). His number is xxx-xxx-xxxx. He seemed quite annoyed, and said it's the third time he has had to call you.