It is necessary to produce a glass suitable for light bulbs; the composition (by weight) is to be 73% SiO2, 17% Na2O, 5% CaO, 4% MgO, and 1% Al2O3. Starting ingredients are sand (which can be assumed to be pure silica), trona, limestone, magnesia, and alumina. Calculate the weight ratio in which they should be fed to the glass furnace.