Question 760080
The cross section of the river is 2*20 or 40 {{{m^2}}}. Now we need to find how many meters the river flows in 3 min, when the rate is 5.4 km per hr.
Let x = the number of meters the river flows in 3 min
First convert the rate from km/hr to m/min by
(1) r = 5.4km*(1000m/km)/((hr)(60min/hr)) or
(2) r = 5400m/(60min) or
(3) r = 90 m/min
Now to find x
(4) x = 3min*90m/min or
(5) x = 270m
The volume, V, of water flowing into the sea is the cross section times the meters it flows in 3 min (our x), 
(6) V = 40{{{m^2}}}*270m or
(7) V = 10,800{{{m^3}}}
Answer:The volume of water flowing into the sea in 3 minutes is 10,800{{{m^3}}}