Forces and equilibrium — practice question

A particle $P$ of mass $0.3\ \text{kg}$ is kept in equilibrium above a horizontal plane by a force of magnitude $5\ \text{N}$ acting vertically upwards. The particle is linked by two strings $PA$ and $PB$ with lengths $0.9\ \text{m}$ and $1.2\ \text{m}$ respectively. The points $A$ and $B$ are on the plane, and angle $APB = 90^\circ$ (see diagram).