Improve the given sentence if necessary. I am waiting for three-quarters of an hour.

If some action has started in the past and is still continuing, then present perfect continuous tense should be used instead of present continuous tense. So, the phrase ‘am waiting’ needs to be replaced with ‘have been waiting’ to make the sentence contextually correct. Thus, the correct formation would be, ‘I have been waiting for three –quarters of an hour’.