Yen read 4 books in 2 h 45 min. She took the same amount of time to read each of the first 3 books. She took 37 min longer to read the fourth book than each of the first 3 books. She finished reading all the books at 19 40. What time did she start reading the fourth book?
Duration that Yen took to read the first book = 1 u
Duration that Yen took to read the second book = 1 u
Duration that Yen took to read the third book = 1 u
Duration that Yen took to read the fourth book = 1 u + 37 min

Total duration that Yen took to read the four books 
= 1 u + 1 u + 1 u + 1 u + 37 min
= 4 u + 37 min

4 u + 37 min = 2 h 45 min
4 u = 165 min - 37 min
4 u = 128 min  

1 u = 128 min ÷ 4 = 32 min

Duration that Yen took to read the fourth book
= 32 min + 37 min
= 69 min
= 1 h 9 min

1 h 9 min before 19 40: 18 31

Time that Yen started to read the fourth book = 18 31

Answer(s): 18 31