A spherical tank with a radius of $0\mathrm{.}75$ m contains air at a temperature of $15$C and a pressure of $210$

kPa. If the tank is heated to $30$C$,$ determine the mass of air that must be removed to keep the tank at

the same pressure. Assume a specific gas constant of Rg $=286\mathrm{.}9$ J$/$kg$-$K for this problem.