What does this symbol indicate on a weather map?

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.

: -)

paper covers rock.

explanation:

rock only smashes scissors.

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.