Note the pattern here.......
20 = 1 person knows at 4:15
21 = 2 more people know at 4:30
22 = 4 more people know at 4:45
23 = 8 more people know at 5:00
.......and note that the sum of the previous terms is always one less than the last term. Therefore 63 + 26 = 63 + 64 = 127. This implies that, starting at 4:15 PM ......6 "blocks" of 15 minutes (= 90 minutes) are necessary to notify 127 students. So, by 5:45 PM, 127 students are notified. This means that one more 15 minute block will be necessary to notify all 176 students = 6:00 PM
