Hi 1to89
So, you are asking a question in which you likely won’t get a definitive answer. Remember, your GMAT score is based on not only the number of questions you answer correct/incorrect, but also the difficulty of those questions, among other things. Thus, there is no way to tell you the exact number of questions you must get correct in order to achieve a 720+ GMAT score.
With all this said, have you taken an official MBA.com practice exam to determine your baseline score? If not, you should take a practice exam ASAP to see how you do. If after taking that practice exam you’d like some further advice, feel free to reach back out.
Also, you may find it helpful to read this article about
How to Score a 700+ on the GMAT.
Good luck!