Simple Harmonic Motion

A mass ' $M$ ' is suspended from a spring of negligible mass. The spring is pulled a little and then released so that the mass executes S.H.M. of periodic time ' $T$ '. If the mass is increased by ' $m$ ', the time period becomes $4 T / 3$, then the ratio of $\frac{\mathrm{M}}{\mathrm{m}}$ is