Michelson used an eight-sided mirror rotating at 528 rev/s in place of the toothed wheel. The distance from the rotating mirror to a distant reflector was 35.5 km. If the light completed the 71.0- km round trip in the time it took the mirror to complete one-eighth of a revolution, what is the speed of light?

I tried using t=d/c but Im not sure how to find c when c=3.00x10^8, please help!