A cylinder of lead has a radius of 4.0cm and a height of 10.0cm. What is the mass of the cylinder of lead?

So lead has a density of 11.34 g/cm^3 according to a quick google search. If this is not the value you are using, just replace what you do use where I put 11.34

knowing the density, if we knew the volume we could find the mass by unit conversion since g/cm^3 * cm^3 = g, so we would multiply the density by the volume. And the question gives us the means to find the volume.

Volume of a cylinder is area of its base times the height. Area of its base, a circle (since it's a cylinder) is π*r^2 where r is the radius and π is roughly 3.14. I will leave π as the symbol until the end so it's easier to deal with.

So volume = area * height = πr^2*h = π4^2*10 = 160π (I moved pi to the back). It's units are cm^3 since both measurements were in cm. You can feel free to multiply π by 160 now if you like. Anyway, now that we have the volume we multiply it by the density. so 160π cm^3 * 11.34 g/cm^3 = 1814.4π g. If you multiply that by 3.14 for π you get 5697.216 g. And there's the mass. Let em know if there was something you didn't understand.