Answer
Observers on earth will measure the traveler to be 3.705 years older.
Work Step by Step
We can use our answer from 13(a) in the time dilation equation to find out how much older observers on earth will measure the traveler to be. Therefore;
$\Delta t=\Delta t_0 / \sqrt{1-\beta^2 }$
$\Delta t=26.26 years / \sqrt{1-0.9900^2 }$
$\Delta t=3.705years$
