Bronze is an alloy made of copper (Cu) and tin (Sn). Calculate the mass of a bronze

Question:

Bronze is an alloy made of copper (Cu) and tin (Sn). Calculate the mass of a bronze cylinder of radius 6.44 cm and length 44.37 cm. The composition of the bronze is 79.42 percent Cu and 20.58 percent Sn and the densities of Cu and Sn are 8.94 g/cm3 and 7.31 g/cm3, respectively. What assumption should you make in this calculation?