Answer:
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Total cost, C = 8x^2 + 12xz
volume, V = (x^2)*z = 10
C = 8x^2 + 12x*10/x^2
= 8x^2 + 120/x
dC/dx = 16x - 120/x^2 = 0
16x = 120/x^2
x^3 = 120/16
x = 1.957 ft
d^2C/dx^2 = 16 +240/x^3 = +ve for x = 1.957
so, C is minimum when
x = 1.957 ft z = 2.61 ft
Length of the base x is 1.957 ft and height of side z is 2.61 ft
One number to the right of the decimal will mean there are two numbers to the left of the decimal.
When rounding to 50 as the nearest ten the number needs to be between 45 and 54.
Using the 3 numbers shown that would be 48.3
