What is equal to three tenths 0.6 0.03 0.2 0.3 0.10

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;

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Matt had 5 library books. he checked out 1 additional book every week without retuening any books. whats the matching equation