If we sketch the shape of the solid, it is a corner of a cube of side length 8. Hence the volume is one-sixth of a cube, Volume = 8^3/6=256/3=85.333...
Or it is a pyramid with triangular base with two faces perpendicular to the base, area of base = 8^2/2=32, height=8, so volume = Ab*h/3=32*8/3=256/3=85.333... as before