Gillian read 4 books in 2 h 29 min. She took the same amount of time to read each of the first 3 books. She took 57 min longer to read the fourth book than each of the first 3 books. She finished reading all the books at 17 13. What time did she start reading the fourth book?
Duration that Gillian took to read the first book = 1 u
Duration that Gillian took to read the second book = 1 u
Duration that Gillian took to read the third book = 1 u
Duration that Gillian took to read the fourth book = 1 u + 57 min

Total duration that Gillian took to read the four books 
= 1 u + 1 u + 1 u + 1 u + 57 min
= 4 u + 57 min

4 u + 57 min = 2 h 29 min
4 u = 149 min - 57 min
4 u = 92 min  

1 u = 92 min ÷ 4 = 23 min

Duration that Gillian took to read the fourth book
= 23 min + 57 min
= 80 min
= 1 h 20 min

1 h 20 min before 17 13: 15 53

Time that Gillian started to read the fourth book = 15 53

Answer(s): 15 53