Let the speed of steamer be x km/hr.
Speed of stream = 1 km/hr.
Downstream speed = (x + 1) km/hr.
Upstream speed = (x – 1) km/hr.
By using the formula
Distance = speed × time
= (x + 1) × 9 and
= (x – 1) × 10
9x + 9 = 10x – 10
9x – 10x = -10 -9
-x = -19
x = 19 km/hr.
∴ The speed of the steamer in still water is 19 km/hr.
Distance between the ports is 9(x + 1) = 9(19+1) = 9(20) = 180 km.