Let's call the capacity of the tank "C" liters. Initially, the tank is 40% full of water, which means it contains 0.4C liters of water. When 9 liters of water are removed, it becomes 1/4 full, which means it contains (1/4)C liters of water. We can set up an equation using this information: 0.4C - 9 = (1/4)C Now, let's solve for C: 0.4C - 9 = (1/4)C Multiply both sides of the equation by 4 to eliminate fractions: 1.6C - 36 = C Subtract C from both sides: 0.6C - 36 = 0 Now, add 36 to both sides: 0.6C = 36 Finally, divide by 0.6 to find the capacity of the tank: C = 36 / 0.6 = 60 So, the capacity of the tank is 60 liters.