i was hoping somebody could give me a hand with a homework problem i have . first here's the question . -> Planet X has two satellites . A and B . Both orbits are circular . Satellite A's orbital radius is 4 times B's orbital radius . calculate the following ratios . a) A's orbital period / B's orbital period b) A's orbital speed / B's orbital speed ----- now i'm kind of stumped because of the lack of information . for a) i know that the ratio of orbital periods is the ratio of the T's . but i'm absolutly losing it trying to figure out how to find the T's . i know that ((4pi^2)/G) (R^3/T^2) ) = M1 + M2 and R^3 = T^2 , also C = 2piR . but i can't for the life of me see how i could get the desired ratio with those formulas . does anybody know if i'm on the right track ? or should i be using some other formula that i'm somehoe missing ?