A particle \(P\) of mass 0.5 kg is moving along the positive \(x\)-axis under the action of a resultant force. The force acts along the \(x\)-axis. At time \(t\) seconds, \(P\) is \(x\) metres from the origin \(O\) and is moving away from \(O\) in the positive \(x\) direction with speed \(\frac { 12 } { x + 3 } \mathrm {~m} \mathrm {~s} ^ { - 1 }\)
Find the magnitude of the force acting on \(P\) when \(x = 3\)