Length Contraction problem
A rocket ship travels to a star 100 light years away, moving at 9/10 the speed of light.
a. As measured by earth clocks, how long will it take the rocket ship to reach the star?
b. As measured by clocks on the rocket ship, how long will it take the rocket ship to reach the star? What principle did you use to obtain your answer?
c. With respect to the earth frame of reference, what is the distance from the earth to the star?
d. With respect to the rockship frame of reference, what is the distance from earth to the star? What principle did you use to obtain your answer?

I'm having trouble with (d). But here's what I have thus far. Let me know if it's incorrect.
For a. I used time = D/v to get 100lightyears/.9c = 111.11 years for the elapsed time on earth.
For b. I used the time dilation principle and multiplied the earth time by the root factor to get 48 years for elapsed time for the rocket.
For c. I have 100 light years.
For d. I'm not sure what to do.. I'm just now learning the length contraction principle. Could someone walk me through this? Thanks.
