Question 1101394
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I assume the 6m is the length of a side of the square base....<br>
The volume of the pyramid (in cubic meters) is one-third base times height:
{{{(1/3)(6^2)(12) = 144}}}<br>
When the tank is filled to 3/4 of its depth (9m, out of the total height of 12m), the volume of water is (3/4)^3 of the volume of the whole tank.<br>
That statement uses the powerful general principle concerning similar figures: if the scale factor is a:b, then the ratio of areas is a^2:b^2, and the ratio of volumes is a^3:b^3.<br>
So the volume of water in the tank when the depth is 9m is 27/64 of the total volume: {{{(27/64)*144 = 243/4}}}<br>
The volume still remaining in the tank is (1-(27/64)) = 37/64 of the total volume of the tank: {{{(37/64)*144 = 333/4}}}<br>
That's the interesting part of the problem.
I leave it to you to convert that volume in cubic meters to gallons, and to find the amount of time it takes to finish filling the tank at 25 gallons per minute.