surface areas and volumes.

find the volume of the frustrum using the formula.

The answer will be in cu cm.

then use 1000 cu cm = 1 lit

 and find how many liters are there in the container.

multiply with the rate Rs. 20/lit

 and that wil be the cost of the milk.

 Next,

 find the  C.S.A. of the frustrum , then add the area of the smaller base (as it's open at the top).

 This will be thet otal surface area.if 100 sq cm cost Rs. 8, then these many sq cm will cost how much?

 Use unitary method.