I have a question that I just do not understand.

It is about a man who has a questionnaire on how he can improve the service of his petrol (gas) station.

The Question:

Dumisani says he is finding it difficult to organise the data he collected for question 2 (below) Some customers say they buy petrol (gas) at Dumisani's every day, some say they only stop at his petrol (gas) station once a month.

a) Can you suggest how Dumisani could classify the data?
b) Rewrite question 2 of the questionnaire (below) so that Dumisani will not have this problem again.

How often do you buy petrol at Dumisani's petrol station.

Please use understandable language for I don't understand what people are answering here most of the time.