Shryi read a 480-page-long bookcover in a single session, at constant raet. After reading for 1.5 hours, she had 402 pages left to read. Let p (t) denote the muber of pages to read P as a function of timet t (measured in hours)

Let's assume the book (not the book cover) is 480 pages long. After 1.5 hours, she had read (480-402) pages: 78 pages in 1.5 hours.

Thus, her reading rate is 78 pages / 1.5 hours, or 52 pages / hr.

Then P = the # of pages left to read = 480 pages - (52 pages/hr) * t