Explanation:
9.80665 N/kg is the force applied by Earth's gravity on a 1 kg of mass (that is then the weight of 1kg mass). the acceleration due to this gravity is usually correspondingly defined as 9.81m/s².
now we have 99 kg.
that means we have to multiply 9.81 by 99
99×9.81 = 971.19 N
if we just roughly round the weight of 1 kg from 9.81 to 10 N, we get then the proposed 99×10 = 990 N result.
but as you can see, this is not very precise.
