1. **State the problem:** We have two alcohol solutions A and B mixed in the volume ratio 1:3. The mixture's volume is doubled by adding more of solution A, making the final mixture contain 72% alcohol. Solution A has 60% alcohol. We need to find the percentage alcohol of solution B. 2. **Assign variables:** Let the volume of solution A initially be $V_a$ and solution B be $V_b$. Given $V_a : V_b = 1 : 3$, so $V_b = 3 V_a$. 3. **Calculate initial volume and alcohol content:** Initial total volume: $$ V_{initial} = V_a + V_b = V_a + 3 V_a = 4 V_a $$ Initial amount of alcohol: $$ A_{initial} = 0.60 V_a + x \times 3 V_a = 0.60 V_a + 3 x V_a $$ where $x$ is the alcohol fraction in solution B (unknown). 4. **After doubling volume by adding solution A:** New volume: $$ V_{final} = 2 \times V_{initial} = 2 \times 4 V_a = 8 V_a $$ Since the volume is doubled by adding solution A only, the added volume is $4 V_a$ of solution A with 60% alcohol. Total alcohol after adding solution A: $$ A_{final} = A_{initial} + 0.60 \times 4 V_a = (0.60 V_a + 3 x V_a) + 2.4 V_a = (0.60 + 3x + 2.4) V_a = (3x + 3) V_a $$ 5. **Final percentage alcohol:** Given final mixture concentration: $$ \frac{A_{final}}{V_{final}} = 0.72 $$ Substitute values: $$ \frac{(3x + 3) V_a}{8 V_a} = 0.72 $$ Simplify: $$ \frac{3x + 3}{8} = 0.72 $$ Multiply both sides by 8: $$ 3x + 3 = 5.76 $$ Subtract 3: $$ 3x = 2.76 $$ Divide by 3: $$ x = \frac{2.76}{3} = 0.92 $$ 6. **Interpret result:** The percentage alcohol in solution B is: $$ 0.92 \times 100\% = 92\% $$ 7. **Answer:** Option C) 92%