You can put this solution on YOUR website! The formula for the volume of a pyramid is
V = (1/3)Bh
where B is area of the base...
Let's put all the units into mm first, so
length = 8 cm = 80 mm
width = 10 mm
height = 3 dm = 300 mm
so B = 80 x 10 = 800 mm^2
and
V = (1/3)(800 mm^2)(300 mm)
V = (100 mm)(800 mm^2)
V = 80000 mm^3