Match the compound with the correct element contained within it.
iron
1. chlorophyll
carbon, hydrogen,
nitrogen, oxygen,
phosphorus, and calcium.
2. hemoglobin
3. 300 enzymes
cobalt
4. 30 enzymes
zinc
5. vitamin b12
magnesium
6. organic compounds such as
carbohydrates, lipids, proteins, and
nucleic acids.
copper

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.

: -)

chert is a sedimentary rock composed of microcrystalline or cryptocrystalline silica. with this little bit of information, you can come to the conclusion that your answer is c.  

explanation:

d. planting trees

the trees take in carbon to make oxygen.