two conducting wires of the same material are to have the same resistance one wire is 21.0 m long and 0.45 mm in diameter if the other wire is 0.28 mm in diameter, how long should it be

Light from the sun reaches the earth in 8.3 minutes. the velocity is 3.00 x 10^8 m/s. how far is earth from the sun? i know how to get to d = (3 x 10^8 m/s)(498 sec). i just don't know how to get from there to the answer being 1.5 x 10^11 m.