1. **State the problem:** Calculate the applied voltage $V_A$ across the entire series circuit shown in Fig.2, which consists of two resistors and two voltage sources of 25V and 15V connected in series. 2. **Formula and rules:** In a series circuit, the total applied voltage $V_A$ is the algebraic sum of all voltage sources considering their polarity. 3. **Apply the formula:** $$V_A = V_1 + V_2$$ where $V_1 = 25$ and $V_2 = 15$. 4. **Calculate:** $$V_A = 25 + 15 = 40$$ 5. **Interpretation:** The total applied voltage across the circuit is 40 volts. **Final answer:** $$\boxed{V_A = 40}$$