2 1- 12=9 (water speed)

2 1+9=30 (return speed)

180/30=6 (time)

2 280/ 14=20 (downstream speed)

280/(34- 14)= 14 (current speed)

(20+ 14)/2= 17 (ship speed)

20- 17=3 (water speed)

3 (25+5)×4= 120 (distance)

120/(25-5)=6 (time)