Oscillations

A point mass is subjected to 2 simultaneous sinusoidal displacements in $x$ -directions, $x_1 (t) = A\sin(\omega t )$ and $x_2 (t) = A \sin \left( \omega t + \frac{2\pi}3 \right)$ .

Adding a third sinusoidal displacement $x_3 (t) = B \sin (\omega t + \phi)$ brings the mass to a complete rest. Find the values of $B$ and $\phi$ .