Well, there are 8 boys and the brother is one of them so 1 is 12.5% of 8 and out of 10 girls, there 1 is the sister and 1 out of 10 is 10%. Now we multiply the percentages to get the answer 1/80
She used 1221 wrapping paper for 21 gifts, so to find the individual amount, you would do: 1221/21 She used about 58.143 ft² of wrapping paper for each gift.