\(\dfrac{AN}{NC}=3\Rightarrow\dfrac{AC}{NC}=4\Rightarrow\dfrac{NC}{AC}=\dfrac{1}{4}\\ \dfrac{S_{BMP}}{S_{ABM}}=\dfrac{BP}{AB}=\dfrac{1}{2}\\ \Rightarrow S_{ABM}=2S_{BMP}=12\left(cm^2\right)\\ \dfrac{S_{AMB}}{S_{AMC}}=\dfrac{MB}{MC}=1\\ \Rightarrow S_{AMB}=S_{AMC}=12\left(cm^2\right)\\ \dfrac{S_{MNC}}{S_{AMC}}=\dfrac{NC}{AC}=\dfrac{1}{4}\\ \Rightarrow S_{MNC}=\dfrac{1}{4}S_{AMC}=3\left(cm^2\right)\)