| p{3cm} p{3cm} p{3cm}} (1) $12$ and $-6$ | (2) $-4$ and $10$ | (3) $9$ and $-3$ | (4) $8$ and $-2$ |
\textbf{177.} Two small identical metal spheres that have equal electric charges are 30 cm apart. The attractive force between them is 4 Newtons. If we bring the two spheres into contact and then separate them, the electric charge of each sphere will be $+3\mu C$. What was the initial charge of the spheres? (in microcoulombs) $\left(k = 9\times10^9\ \dfrac{\text{N.m}^2}{\text{C}^2}\right)$
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\begin{tabular}{p{3cm} p{3cm} p{3cm} p{3cm}}
(1) $12$ and $-6$ & (2) $-4$ and $10$ & (3) $9$ and $-3$ & (4) $8$ and $-2$
\end{tabular}
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