The more you study for the definite exam; the better will be the performance on it. If you study for ten hours, your score will be 65%. If you study for twenty hours, your score will be 95%. You can get as close as you wish to the perfect score just by studying long enough. Suppose the percentage score is the linear-to- linear function of number of hours which you study. If you wish the score of 80%, how long do you require to study?