From formula we get redius^3 = (period^2*(mass of Mars)*(Gravitational acceleration)))/4*pi^2 From Into this equation put period = 8.86 * 10^4 sec, mass of mars = 6.39*10^23 kg ,Gravitational acceleration= 6.67*10^-11 and pi = 22/7 and get value of r which is 2.7 * 10^7 meters