First, we need to compute the volume of the hemicylinder with a diameter of 100 ft (radius 50 ft) and a height of 1/3 ft, as follows:

Next, we need to compute the volume of the hemicylinder with a diameter of 80 ft (radius 40 ft) and a height of 1/3 ft, as follows:

Finally, the volume of concrete needed to build the driveway is 1308.33 - 837.33 = 471 cubic feet