Help me with this pls

In triangle abc segment de is parallel to the side ac . (the endpoints of segment de lie on the sides ab and bc respectively). find de, if ac=20cm, ab=17cm, and bd=11.9cm;

Find the greatest common factor of the followig monomials 21u^5v,3u^4v^6, and 3u^2v^5

Which of the following quartic functions has x = –1 and x = –2 as its only two real zeroes?