Two identical balls made of pure iron and copper having diameter of 6 cm and initial temperature of 500°C are being cooled in oil having temperature of 100°C and heat transfer coefficient of 10 W/m2K....

Two identical balls made of pure iron and copper having diameter of 6 cm and initial temperature of 500°C are being cooled in oil having temperature of 100°C and heat transfer coefficient of 10 W/m2K. It is desired that both balls should reach a temperature of 150°C at same time. Which ball should be inserted into oil first? After how much time second ball should be inserted into oil?