Let B and G be the number of gifts the boys and girls wrapped. Total number of gifts wrapped is B+G.
We can write the equation, G=2B/5.
If each boy, b, wrapped 20 more gifts than each girl, and each girl wrapped g gifts then b=g+20.
5 boys wrapped 5b=5(g+20) gifts. 6 girls wrapped 6g gifts.
So G=6g and B=5(g+20). G=2B/5=2(g+20)=6g. So 6g=2g+40, 4g=40 and g=10.
Now we know that each girl wrapped 10 gifts and each boy 20 more=30 gifts.
B=5(g+20)=150 and G=60. We also know that B+G=210, the total number of gifts wrapped.
B-G=90; all the boys wrapped 90 more gifts than all the girls.
CHECK
Now rewrite the question with actual amounts:
The girls wrapped 60 gifts in all, which is 2/5 of 150, the total number of gifts the boys wrapped. Each boy wrapped 30 gifts, which is 20 more than each girl wrapped. The total wrapped by the boys is 150-60=90 more than the girls.