Andrea Bocelli’s greatest songs of all time

"That Which Remains" by Andrea Ramsey

SOLVED: A set of twins, Andrea and Courtney, are initially 10 years old. While Courtney remains on Earth, Andrea rides on a spaceship that travels away from Earth at a speed of 0.70c for 15 years (as measured by Courtney). At the end of the trip, Courtney is 25 years old. How old is Andrea?