homework and exercises - How large of a solar sail would be needed to travel to mars in under a year?

I'm attempting to approach this using the identity $$F/A = I/c$$ I can solve for Area easily enough $$A = F(c/I)$$ and I know the distance $d$ is $$d=1/2(at^2)$$

But I'm having difficulty trying to relate this to the time it would take to reach mars.

Any ideas where to go from here?

Answer

You've done the two hard parts: (1) relate area to force and intensity and (2) relate distance, acceleration, and time. For connecting these two, I suggest looking at Newton's second law.