### Solution:

In this question, we are asked to find the amount of water that falls into the sea per minute when the river is 3 m deep and 40 m wide and flows at a speed of 2 km per hour.So before proceeding we need to know the following conversions to go further to get Ans as:

1km=1000m

1 hour = 60 minutes

So we get the speed of the river in meters per minute as:

$\n \n 2\xd7\n \n 1000\n \n 60\n \n =\n \n 100\n 3\n \n \n $

So, we get the length that the river covers in one minute as $\n \n \n \n 100\n 3\n \n m\n $ .

Also in the question, the width is 40m and the height is 3m.

Now using the V cuboid volume formula, since the river flows in this shape, you get the volume of the river as:

$\n \n V=l\xd7b\xd7h\n $

Then, by substituting the value of length l as $\n \n \n \n 100\n 3\n \n m\n $ , breadth b as 40m and height h as 3m, we get the volume of river as:

$\n \n \n \n V=\n \n 100\n 3\n \n \xd740\xd73\n \n \n \n \n \u21d2V=4000\n m\n 3\n \n \n \n \n \n \n $

So we get the volume of water in the river as 4000 cubic meters.

Now in the question we are asked to get the volume in liters for which we need another conversion between meter cube and liter as:

$\n \n 1\n m\n 3\n \n =1000l\n $

So, by using the above conversion, we get the amount of water in litres for 4000 metre cube as:

$\n \n \n \n 4000\n m\n 3\n \n =4000\xd71000l\n \n \n \n \n \u21d24000\n m\n 3\n \n =4000000l\n \n \n \n \n $

Hence, we get the amount of water falling into the sea per minute as $\n \n 4000000l\n $ .

So, option 1 is correct.