John has a fish tank with base dimensions 72 cm by 48 cm and height 52 cm. He fills it with water to two-thirds of the height. He places a cube into the tank and the water level rises to three-quarters of the height of the tank. Without removing the cube, he then places a trapezoidal prism into the tank. 500 millilitres of water spills. Given that 1 millilitre = 1 cm³, find

(a) the length of the side of the cube,
(b) the height of the trapezoidal prism if its cross-sectional area is 928 cm². Give your answers correct to 3 significant figures.​