The way to solve this is by putting each distance in terms of the same exponent, let that be 10¹⁵
The first becomes 176 × 10¹⁵
The second becomes 221.3 × 10¹⁵
The third becomes 3.1452 × 10¹⁵
The fourth remains 125.5 × 10¹⁵
It is now visible that the third and fourth stars are closest to the Earth and those should be the ones chosen for study.