How to compute volume of a rectangle?

Question
A rectangular piece of a plastic is half as wide as it is long from each corner a 3cm square is cut out, and the ends are turned up as to make a box whose contents are 90 cubic cms what would be the volume of this box if filled to a depth of 1/10 cms.



Solution
To compute for the volume of a rectangle, the formula is Side1*Side2*Side3 OR L*W*H
where
L = length
H = height
W = width
For the given rectangle, we have
L = L
H = H
W = 2L
Volume = 90 cubic centimeter
which is equal to L*2L*H
therefore, the height of the rectangle is
45
----
L^2
and the length of the rectangle is
the square root of 45/H

Given that the height is 1/10 centimeter, then
Length = 21 centimeters
Width = 42 centimeters

Therefore the volume of the rectangle is 88 cubic centimeters

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