Its "C" because without oxygen you can't have fire
To combine like terms and single out one term to take it easier to solve, the 6x was moved to the other side to combine like terms.
Subtracting 6x from 10x which is 4x
Answer:

Step-by-step explanation:
To evaluate or simplify expressions with exponents, we use exponent rules.
1. An exponent is only a short cut for multiplication. It simplifies how we write the expression.
2. When we multiply terms with the same bases, we add exponents.
3. When we divide terms with the same bases, we subtract exponents.
4. When we have a base to the exponent of 0, it is 1.
5. A negative exponent creates a fraction.
6. When we raise an exponent to an exponent, we multiply exponents.
7. When we have exponents with parenthesis, we apply it to everything in the parenthesis.
We will use these rules to simplify.

42 - -84=-42
Hope this helps :)