\text{Nice and easy $\frac{\text{stand}}{2}$}

\text{500 K}

\text{400 K}

|W|

|Q_H|=540\hspace{1mm} J

|Q_L|=400\hspace{1mm} J

|Q_H|=500\hspace{1mm} J

|W|=120\hspace{1mm}J

|W|

|Q_H|

|Q_L|

|Q_L|

\text{Engine } 1

\text{Engine } 2

\text{Engine } 3

C_3

C_2=12\hspace{1mm}\mu F

C_1=4.0\hspace{1mm}\mu F

C_3=2.0 \hspace{1mm}\mu F

C_1

C_2

\begin{aligned} &\mathrm{C}_{\mathrm{f}}=\kappa \mathrm{C}_{\mathrm{i}}=6.5 \times 13.5=87.75 \mathrm{pF}\\ &\text { Charge is conserved: } Q=C_i V_i=13.5 \times 12.5=168.75 p C\\ &U_f=\frac{Q^2}{2 C_{\mathrm{f}}}=\frac{\left(168.75 \times 10^{-12}\right)^2}{2 \times 87.75 \times 10^{-12}}=1.62 \times 10^{-10} J=162 \times 10^{-12} J=162 \mathrm{pJ} \end{aligned}