Here's the third one:
3.The reservoir is in the form of the frustum of an inverted square pyramid with upper base edge 24m, lower base edge 18m and altitude 3m. how many hours will it require for an inlet pipe to fill the reservoir if water flows in at the rate of 200 liters per min.
The area of the upper base (A1) is [24m]^2 = [2400cm]^2
The area of the lower base (A2) = [18m]^2 = [1800cm[^2
The total volume is :
(1/3)(altitude) [ A1 + A2 + sqrt( A1 * A2) ]
(1/3)(3)( 2400^2 + 1800^2 + sqrt [ 2400^2 * 1800^2] ) = 13,320,000 cm^3
And 200 liters = 200,000cm^3
So....it takes...... [13,200,000 / 200/000] = 66 min = 1.1 hr to fill the tank
