A tank with rectangular base and rectangular sides, open at the top is to be constructed so that its depth is  `2m` and volume is `8 m^3` . If building of tank costs `Rs. 70` per sq. metre for the base and `Rs. 45` per sq. metre for sides, what is the cost of least expensive tank?

Explanation

The volume of the tank is

`2xym^3=8`

`2xy=8`

`impliesxy=4`

`impliesy=4/x`

Base area=`xy=x(4/x)=4m^2`

Area of four sides=`2xx2(x+y)=4(x+4/x)`

Let C be the total cost

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