17° 31′ 23 – 12° 23′ 45″ = …..?

17° 31' 23"
12° 23' 45" _
  5°  7' 38"

17°31'23"
12°23'45"
__________ –
17°(31-1)'(23+60)"
12° 23' 45"
__________________ –
17°30'83"
12°23'45"
__________ –
5°7'38"