The more you study for the certain exam, better your 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, p(n) , is the function of number of hours, n, which you study in form p(n)=(an+b)/ (cn+d). If you wish the score of 80%, how long do you require to study?