To find a percentage of a number, turn the percent into a decimal by dividing by 100, then multiply that decimal by the number.
82 ÷ 100 = 0.82
0.82 × 950 = 779
Now, to find the number of seats not occupied, you subtract the percentage that is occupied from the whole.
779 is 82% of 950, so 779 will be subtracted from 950
950 - 779 = 171
171 seats are not occupied.