The other investor who owns 30% is not asking for this. I own 50% equity. I have been taking care of the day to day runnings of the business as CEO and Founder.
Normally an investor has the right to inspect the accounting books. But he needs to ask it in a formal manner with a letter, he cannot just come and ask for the books you could tell I do not have them ready for you. Be careful this is normally an atypical situation (as numbers are reviewed during the shareholders meetings) and i strongly suggest that you consult your company's lawyer and use him to follows this case. Laws can be slightly different depending states and companies bylaws.