Answer
Ans $\text{Radius = 0.070338 m}$
Work Step by Step
$\text{Tension = 120 N}$
Also
$$\text{Tension} = M\times g$$
But
$$M = \rho\times\ Volume$$
Here
$\rho = 8400 \frac{kg}{m^{3}}$
$\text{Volume} = \frac{4}{3}\pi R^{3}$
$$\therefore\text{Tension} = \rho\times \frac{4}{3}\pi R^{3}\times g$$
$$\frac{\text{Tension} \times 3}{4\times\pi\rho \times g} = R^{3}$$
$$R =(\frac{\text{Tension} \times 3}{4\times\pi\rho \times g})^{\frac{\textbf 1}{\textbf 3}} $$
$\therefore\text{R = 0.070338 m}$
