Erika read 3 books in 2 h 19 min. She took the same amount of time to read each of the first 2 books. She took 31 min longer to read the third book than each of the first 2 books. She finished reading all the books at 15 20. What time did she start reading the third book?
Duration that Erika took to read the first book = 1 u
Duration that Erika took to read the second book = 1 u
Duration that Erika took to read the third book = 1 u + 31 min

Total duration that Erika took to read the three books 
= 1 u + 1 u + 1 u + 31 min
= 3 u + 31 min

3 u + 31 min = 2 h 19 min
3 u = 139 min - 31 min
3 u = 108 min  

1 u = 108 min ÷ 3 = 36 min

Duration that Erika took to read the third book
= 36 min + 31 min
= 67 min
= 1 h 7 min

1 h 7 min before 15 20: 14 13

Time that Erika started to read the third book = 14 13

Answer(s): 14 13