Suppose that the cost of a paving stone is $2.50 plus $.18 for every 4 in.³ of concrete how much would each paving stone cost ?

We need to know the dimension of the paving stone.

For example, the paving stone is shaped like a rectangular prism with the following dimension.

Length = 10 inches
Width = 3 inches
Height = 2 inches

Volume of a rectangular prism = Length * Width * Height
V = 10 in * 3 in * 2 in
V = 60 in³

60 in³ / 4 in³ = 15

cost of paving stone = 2.50 + .18(15) = 2.50 + 2.7 = 5.20 per paving stone.

What do you mean by that?