All months have 28 days (and more) but only February is 28 days long in normal years and 29 days long in leap years. However, all twelve months in a year have up to 28 days. Others apart from February on normal years just extend beyond those 28 days.
The Gregorian calendar has seven months that have 31 days and four months that have 30 days. January, March, May, July, August, October, and December consist of a total of 31 days every year. April, June, September, and November have 30 days every year. All these days sum up to the 365 days a year in common years and 366 days a year in leap years.
So, unless you are asked how many months are 28 days long, the answer to this question is 12. But note that it is only one month that is 28 days long. Therefore, ensure you pay close attention to the phrasing of the question. It would help you give an accurate answer.