To solve the quadratic equation \( 84x^2 + 16x = 0 \), we can factor out the common term:
\[ x(84x + 16) = 0 \]
Setting each factor to zero gives us:
- \( x = 0 \)
- \( 84x + 16 = 0 \)
Now, solving for \( x \) in the second equation:
\[ 84x + 16 = 0 \ 84x = -16 \ x = \frac{-16}{84} \ x = \frac{-2}{10.5} \ x = \frac{-2}{\frac{21}{2}} \ x = \frac{-4}{21} \]
Thus, the solutions to the equation are:
\[ x = 0 \quad \text{and} \quad x = \frac{-4}{21} \]
The correct answer that resembles this solution is \( x=0 \) and \( x=-421 \), given that the last solution simplifies to that in context is incorrect.
None of the provided responses match the correct solutions. Therefore, the quadratic equation has answers \( x=0 \) and \( x = -\frac{4}{21} \). Please check the options provided or clarify further.