questioner wrote:

I think the correct answer to this question is option E. Why can't the required number be 940 or 960 and why zero has been assumed as the units digit?

When we use the both statements together the required number can be any number from 934 to 966, including 940 and 960. Any one of these numbers has 9 as the hundreds digit. The question doesn't ask us to find the exact number, but just to find what its hundreds digit is. Using the both statements we are sure that this digit is 9.