Viruses tend to be specific in the cells they infect. which of the labeled structures would assist the virus in infection of the proper host cell.

nucelocapsid

envelope proteins

viral genome

viral tegument

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.

: -)