(20ly)/(20.5) = 0.97c
Using that, I solved for T to get 4.8 years. About 5 years to the astronaut's age is 31, and the son is 24.5, the difference is 7 then. I think this is correct.
Homework Statement
A 26 year-old biologist makes a trip to study alien life forms in a distant planet 10 light-years away. The round trip including a stay of 1 year in the distance planet takes 21.5 years according to the clock on earth. The biologist’s son is 3 year-old when she left. Assume...