Volume (V) = Length (L) multiplied by Width (x) multiplied by Height (H)
V = L*x*H [simplify]
V = (x+2) * x * (x-1) [L = width +2] [Height = width -1]
[substitute values for Length and Height in terms of x, as given in the equation]
[This is the final expression in terms of x]
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V (3+2)'*3'*(3-1)' [substitute numeric value for x, as given in the equation]
V = (5)'*3'*(2)' [simplify, according to Order of Operations]
V = 30' [multiply]
V = 30 cu. ft. of soil needed [Volume is a "cubic" measurement (Length*Width*Height or Depth), as opposed to
a "square" measurement such as Area (Length*Width)]