4 ms·I actually figured 91 = 70 + 21 = 10 * 7 + 3 * 7by andr 19y agoI actually figured 91 = 70 + 21 = 10 * 7 + 3 * 7andr 19y agoIt's funny that I get upvoted for possessing 3rd grade arithmetic skills.dreish 19y ago3rd grade in Bulgaria, maybe. To us Americans, that's like an amazing magic trick.