Which process involves the movement of molecules across the plasma membrane from areas of high to low concentrations without any assistance or energy from the cell?

i think it is osmosis

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.

: -)

satellites are frequently used to make observations of the orbit on earth