Question

Express this is scientific notation

Answer 1

Place the decimal point right after the first nonzero digit, which is 3. 

So you'll go from this $0.003045$ to this $3.045$ after this move.
 
Now ask yourself: "how many spots must I move the decimal point to get back to 0.003045?"

The answer is "3 spots to the left"

The exponent of the final answer is -3
The negative indicates "move left" and the 3 tells us how many places to move the decimal

Therefore, $0.003045 = 3.045 \times 10^{-3}$

Answer: Choice C)
This is assuming you meant to write the -3 as an exponent