The maximum number of points Jeff can get is 100. (25 * 4) However, for each question he gets wrong, he's actually losing 6 points because he doesn't get the four points for getting right, and has the additional -2 points for getting it wrong. Since he only got a score of 70, that means he lost 30 points.
30/6 = 5. So he missed 5 question and got 20 question right.
