Im just guessing here, but that 4.1eV could be the energy that would be absorbed by the mirror, as any photon with a higher energy may be sufficient to be absorbed to release a photoelectron. So with the maximum energy for reflection, we can work out the minimum wavelength for reflection via wavelength=hc/E. So I think it may be relevant - there doesnt seem to be anywhere else to go from.
As for the second part, you could calculate the momentum of the photon by (mv)=h/wavelength. Then with the momentum and f=mv/t, use the speed of light and divide that by the seperation 10^-6, you will be left with a value in the units s^-1, then multiply the momentum by this value to get the force.
I hope this helped, not sure if it is right at all - but I thought I'd have a shot.