178. Three point charges are placed according to the figure below. The magnitude of the electric field at point M is how many newtons per coulomb? $$\left(K = 9\times10^9 \,\frac{\text{N.m}^2}{\text{C}^2}\right)$$ [Figure: Point M is located 6 cm above the midpoint of a horizontal line. $q_1 = 12.5\,\mu\text{C}$ is on the left end, $q_2 = -12.5\,\mu\text{C}$ is on the right end, each 8 cm from the center, and $q_3 = 7.2\,\mu\text{C}$ is at the bottom center.]
[(1)] $18\sqrt{2}\times10^6$
[(2)] $6\sqrt{2}\times10^6$
[(3)] $6\times10^6$
[(4)] $18\times10^6$
\textbf{178.} Three point charges are placed according to the figure below. The magnitude of the electric field at point M is how many newtons per coulomb?
$$\left(K = 9\times10^9 \,\frac{\text{N.m}^2}{\text{C}^2}\right)$$
\textit{[Figure: Point M is located 6 cm above the midpoint of a horizontal line. $q_1 = 12.5\,\mu\text{C}$ is on the left end, $q_2 = -12.5\,\mu\text{C}$ is on the right end, each 8 cm from the center, and $q_3 = 7.2\,\mu\text{C}$ is at the bottom center.]}
\begin{itemize}
\item[(1)] $18\sqrt{2}\times10^6$
\item[(2)] $6\sqrt{2}\times10^6$
\item[(3)] $6\times10^6$
\item[(4)] $18\times10^6$
\end{itemize}