A river 3 m deep and 40 m wide is flowing at the rate of 3 km/h. How much water will fall into sea in 3 minutes ?

$18000\, m^3$

Area of river = depth × width

= 40 ×3

= 120

Amount of water that flow in 1 minute= 120 × 3 × \(\frac{1000}{60}\)= 6000

Amount of water flow in 3 minutes = 6000 × 3

= 18000

The correct answer is option (3) : $18000\, m^3$