Which of these is not function of the respiratory system?

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.

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.

: -)