Using the Ideal Gas Law:
\(pV=nRT\iff n=\dfrac{pV}{RT}\)
Calculating the ratio between the initial and the final numbers of moles:
\(\dfrac{n_1}{n_2}=\dfrac{\dfrac{p_1V_1}{RT_1}}{\dfrac{p_2V_2}{RT_2}}\)
The statement says that \(T_1=T_2,~p_1=p_2\). Hence:
\(\dfrac{n_1}{n_2}=\dfrac{V_1}{V_2}\iff \dfrac{n_1}{3.8\times10^{-4}}=\dfrac{230}{860}\iff\\\\ n_1=\dfrac{3.8\times10^{-4}\times230}{860}\iff\boxed{n_1\approx1.0\times10^{-4}~mol}\)
