Significant to four figures: 3.682417

If you are rounding to four significant digits, then it should just be 3.682

If you have to round a number to 4 significant figures you have to see if the number next to forth digit is lower than five or higher than five if the number is five or higher than five than you have to round up if the number is lower than five than you have you round down.
For example- 3.682417 the number next to forth digit is lower than five so you have to round down so we are left with 3.682

1.989×10^30 kg is the weight of the sun.

Carbon-14 has a half-life of 5,730 years and most igneous rock is older than that.