A mass weighing 4 lb stretches a spring 1.5 in. The mass is given a positive displacement of 2 in from its equilibrium position and released with no initial velocity. Assuming that there is no damping and that the mass is acted on by an external force of 2 cos 3t lb, formulate the initial value problem describing the motion of the mass. Solved this to find: u"+256u=16cos(3t)then solved this to: u=(151/1482)cos(16t)+(16/247)cos(3t ).Need help with:If the given external force is replaced by a force 4 sin?t of frequency ?, find the value of ? for which resonance occurs.