Help me at least with one exercise

Calculate:

a) The density of the gasoline knowing that a 500 L drum has a mass of 430 Kg.
b) The mass of a piece of glass with a volume of 10 cm3, knowing that the density of the glass is 2.2 g/cm3.
c) The volume of a steel ball of 14 g of mass if the dsteel = 5500 Kg/m3.
d) The mass of 1 L of olive oil (d= 0,85 g/cm3).

Athin electrical heater is inserted between a long circular rod and a concentric tube with inner and outer radii of 20 and 40 mm. the rod (a) has a thermal conductivity of ka = 0.15 w/(m*k), while the tube (b) has a thermal conductivity of kb = 0.8 w/(m*k) and its outer surface is subjected to convection with a fluid of temperature t= -15°c and heat transfer coefficient 60 w/(m2 *k). the thermal contact resistance between the cylinder surfaces and the heater is negligible. (a) determine the electrical power per unit length of the cylinders (w/m) that is required to maintain the outer surface of cylinder b at 15°c. (b) what is the temperature at the center of cylinder a?