for problem (a) it should be 3dv/dt +2v =0. For problem (c) it should be 2d^v/dt^2 +12dv/dt + 18v =0 with initial conditions: at t=0 dv/dt=1 and v=1. problem (d) is d^2x/dt^2 +5dx/dt +6x =0 with initial conditions: at t=0 dx/dt=1 and x=0