By himself, a person can mow his lawn in 48 minutes. If his daughter helps, they can mow the lawn together in 40 minutes. How long would it take his daughter to mow the lawn by herself?

Step 1 ：Let x be the time it takes for the daughter to mow the lawn by herself.

Step 2 ：Set up the equation: \(\frac{1}{48} + \frac{1}{x} = \frac{1}{40}\)

Step 3 ：Solve for x: \(x = 240\)

Step 4 ：\(\boxed{240}\) minutes is the time it would take the daughter to mow the lawn by herself.