Which of the following two cycles are the most closely related in their role in sustaining life? a. carbon and nitrogen b. water and nitrogen c. carbon and oxygen d. nitrogen and phosphorus

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.

: -)