To find the volume of the concrete, we need to convert the thickness from inches to feet. Since 1 foot is equal to 12 inches, 6 inches is equal to 6/12 = 0.5 feet.
Now, we can calculate the volume of the concrete by multiplying the length, width, and thickness:
Volume = Length × Width × Thickness
= 30 ft × 8 ft × 0.5 ft
= 120 ft³
Therefore, the volume of the concrete is 120 cubic feet.
The correct answer is C. 120 cu ft.