The question is asking for the number of bricks required to build the outer structure of a sump. It`s important to note that the dimensions given for the outer sump and each brick are in meters and centimeters, respectively.

To get the total volume of the outer layer that the bricks will cover, we must subtract the volume of the inner sump (6m x 5m x 4m) from the volume of the outer dimension (6.2m x 5.2m x 4.2m). Similarly, to find the volume of the bricks, we multiply their dimensions (20cm x 10cm x 5cm), but remember to convert them into meters first, because volume calculation needs to have the same units.

Then, we divide the total volume of the outer layer by the volume of one brick to get the total bricks that can fit. We get an approximate number, 15408, which is closest to option 3.

Options 1, 2, and 4 provide different quantities of bricks. However, without any complex calculations, it`s clear that these numbers are too low or too high to be accurate, based on the dimensions given for the sump and the bricks.