Richard P. answered 07/02/14
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A special solution can be fairly easily guessed. It is
f = (1/(w -k)) cos(kx -wt) + C.
To this we would have to add a general solution to the homogenous equation df/dx + df/dt = 0
This general solution looks like A exp( i(x - t)) + B exp(-i(x -t)) for constants A and B.
This question looks like it comes from physics with k being a wavenumber and w being a frequency.
However, there seems to be a dimensional inconsistency as the PDE is written.