Hi There,
The answer is not invalid it is correct.
Steps
1.Do 40.00 - 20.59 because there is a negative number in the problem, and in the problem you have to add.
2. You're answer should be $19.41 after you solve step one because you have to subtract. The answer is a positive because the negative number is shorter than the positive number.
So, the answer should be $19.41, there is nothing wrong in the problem.
Hope This Helps :)
