Which level on the energy pyramid has the third most energy?
a. primary producers
b. primary consumer
c. secondary consumers
d. tertiary consumer

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.

: -)

i think its the first one

oxygen +1 most likely