First you would divide your weight on Earth by 9.8m/s which is the gravitational constant. This would give you your mass which would be 10.2 kg. To find the gravity of the unknown planet you would multiply 9.8m/s by 15 which would be 147m/s. Since weight is defined as mass times gravity you would substitute the mass you found earlier and multiply it by the new gravity. This would give you 10.2kg times 147 m/s which equals 1,499.4 lbs or 1,500 lbs if rounding.