Answer:
20 cubic feet.
From feet: length (ft) × width (ft) × height (ft) = cubic feet.
From inches: length (in) × width (in) × height (in) ÷ 1728 = cubic feet.
From yards: length (yd) × width (yd) × height (yd) × 27 = cubic feet.
If you need to convert to cubic feet from inches: divide the final number (i.e. the total you get after multiplying the three dimensions together