An astronaut who was 30 years old left to explore the galaxy in 2020, on a spaceship
travelling at 2.5 x 108 m/s. he is expected to return in 2060. about how old will he appear to be?

52.1 years .  

Explanation:

The time interval from 2020 to 2060 = 40 years. This will be the time as measured by an observer on earth.

For the person who is travelling at v = 2.5 × 10⁸ m/s,

t =40 √(1 - [(2.5 × 10⁸)² / (3.0 × 10⁸)²] = 22.1 years

Actual age for his counterpart on earth would be 30 + 40 = 70 years,

But space travel  makes the astronaut to age slowly (time dilation) . So he appears to be 30 + 22.1 = 52.1 years old.

asthenosphere and convection