The correct answer is E.
There are not enough info to answer the question.
A 840 cubic meters rectangle is built from: height*length*width.
From the question we know the volume of the pool and the filling rate.
A pool can have a a height of 10*width8.4*length10 and have a volume of 840 cubic meters, and it can have a height of 1 meter, width of 100 meters and length of 8.4. In both cases the pool will fill up in a different rate.

A qualitative approach to this one would be to imagine a 1 meter by 1 meter opening that's 840 meters deep. How much water is flowing in to raise the water level 0.5 meters per minute?

Then imagine a giant 40 meter by 21 meter pool that's only 1 meter deep. How much water does it take to raise the water level in that pool 0.5 meters? Put another way, how long will it take to fill if you raise the water level 0.5 meters per minute?

Since one pool fills in 2 minutes and the other takes... quite a bit longer... but they both have the same volume, you know you need more information.

I can only get H ... so Info is not sufficient

This question is more about thinking than about actually solving

We are given the volume of the tank = 840 cubic meters.
Or 840 = L*B*H of the pools

Further, we are told that the water is rising at the rate of 0.5 meters per minute.
We have some information about the height, but absolutely none about the length and the breadth

The pool can have different sizes:
(l,b,h) = (84, 10, 1) or (42, 10, 2) or (1, 1, 840) and so on.
The time required to fill the tank will be different in each of the cases. Hence the information provided is not sufficient

Correct Option: E

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