An ideal monatomic gas undergoes the thermodynamic cycle \(A \rightarrow B \rightarrow C \rightarrow A\) shown in the \(P\)-\(V\) diagram. Process \(A \rightarrow B\) is isochoric heating, process \(B \rightarrow C\) is a linear expansion, and process \(C \rightarrow A\) is an isobaric compression. The state parameters are \(P_A = 100 \text{ kPa}\), \(P_B = 400 \text{ kPa}\), \(V_A = V_B = 2.0 \times 10^{-3} \text{ m}^3\), and \(V_C = 6.0 \times 10^{-3} \text{ m}^3\). What is the thermal efficiency of this engine cycle?