2.4% of 30 answers correct is less than one correct answer or just over 2 points. To estimate your grade percentage may require taking into account the performance of other students for comparison, and we don't have this information. Alternatively, grading could be simply based on percentage, with grades allocated to blocks of percentages: grade A may be 80%-100%, B 60%-79%, C 40%-59%, D 20%-39% and E 0-19%. In this case your grade would be E. You have already given your grade as a percentage based on 30 correct answers, or 90 points, representing 100%.