density

[shrewd juniper]

you have radius (7) so substitute that into the top equation to get the volume of the sphere
Density = Mass/Volume
You want mass
So mass = density * volume
Multiply the value given for density and the value you calculated for the volume of the sphere together to get the mass of the sphere
Pay attention to the units; bc the value you get will be in grams and it's asking for it in kilograms, so divide your final answer by 1000