Lynn read 4 books in 2 h 53 min. She took the same amount of time to read each of the first 3 books. She took 49 min longer to read the fourth book than each of the first 3 books. She finished reading all the books at 21 35. What time did she start reading the fourth book?
Duration that Lynn took to read the first book = 1 u
Duration that Lynn took to read the second book = 1 u
Duration that Lynn took to read the third book = 1 u
Duration that Lynn took to read the fourth book = 1 u + 49 min

Total duration that Lynn took to read the four books 
= 1 u + 1 u + 1 u + 1 u + 49 min
= 4 u + 49 min

4 u + 49 min = 2 h 53 min
4 u = 173 min - 49 min
4 u = 124 min  

1 u = 124 min ÷ 4 = 31 min

Duration that Lynn took to read the fourth book
= 31 min + 49 min
= 80 min
= 1 h 20 min

1 h 20 min before 21 35: 20 15

Time that Lynn started to read the fourth book = 20 15

Answer(s): 20 15