volume

*** edited ***

Area of triangular ends  *  'depth' = volume

Area of a right triangle = 1/2  leg1 * leg2        need to find leg 2  via pythagorean theorem

sqrt (20.5² -13.3² )=  leg2 = 15.6 mm

Area = 1/2  13.3 * 15.6 = 103.74 mm²

 Now multiply by depth of 16 mm              = 1659.84 mm³