Adriveway is 81 ft. long, 6 ft. wide and 4 inches deep. how many cubic feet of concrete will be required for the driveway

The equation for volume is v = length x width x height.  We are given all of these, however one of the measurements is in different units than the others, so we need to convert the units before we do our multiplication...

4 inches x 1 ft / 12 in = 4/12 = 1/3 ft

Now we can multiply our equation...

v = length x width x height
v = 81 x 6 x 1/3
v = 486/3
v = 162 cubic feet

First the units must all be in feet.
4 inches has to be converted to feet 
4 inches x 1ft/12 inches = 4/12 ft = 1/3 ft

The driveway is a rectangular prism.
Area = length x width x height
Area = 81 ft x 6 ft x 1/3 ft = 162 cubic feet