Erika read 4 books in 2 h 3 min. She took the same amount of time to read each of the first 3 books. She took 39 min longer to read the fourth book than each of the first 3 books. She finished reading all the books at 18 16. What time did she start reading the fourth 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
Duration that Erika took to read the fourth book = 1 u + 39 min

Total duration that Erika took to read the four books 
= 1 u + 1 u + 1 u + 1 u + 39 min
= 4 u + 39 min

4 u + 39 min = 2 h 3 min
4 u = 123 min - 39 min
4 u = 84 min  

1 u = 84 min ÷ 4 = 21 min

Duration that Erika took to read the fourth book
= 21 min + 39 min
= 60 min
= 1 h

1 h before 18 16: 17 16

Time that Erika started to read the fourth book = 17 16

Answer(s): 17 16