Is sharks and crocodiles closely related

More recent phylogenetic analyses, based on mitochondrial DNA, have suggested that the crocodile shark is closely related to either the megamouth shark or the sand sharks (Odontaspididae).

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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i thinking chemical change