LINUX SED ONLY 1 command line

1. print the file, but with numbers printed in the SI format ex: 3,400,402.23 -> 3 400 402,23 (comma to space, and period to comma)

2.print only lines with continent data, population density of Antarctica to 10. Dont use 0.00018 in answer , instead select Antarctica and the correct field to change.

3. print only lines with continent data, but the 3 input fields in reverse order. (3,2,1) output fields separated by colon (:)

file.txt:

Continent;Area(sq. mi);Density(People per sq. mi)

Asia;16,920,000;225 Africa;11,730,000;76 North America;9,460,000;54 South America;6,890,000;54 Antarctica;5,300,000;0.00018 Europe;3,930,000;181 Australia;3,478,200;9.3

===========================