Iron density 7874kg/m^3
Volume 30m sphere (assuming 30m is diameter): Pi/6*(30m)^3 gives Pi*4500m^3 volume.
Mass = Pi*4500m^3*7874kg/m^3 (using 355/113 for Pi) = 111,316,061kg.
This is about the weight of the Battleship Missouri (which is bigger, but hollow.)
Pardon me, but it appears that you've computed the mass of a sphere with a 30m radius, not a 30m diameter...unless perhaps I'm missing something? Volume is 4/3rds pi*(r^3), yes?