I see a few ways to solve this:

19 - not taking into account the erroneous prior examples. This is the most classicly correct answer.

40 - by folloing the implicit formula of adding the prior answer to the next line

56 - by doing: a + (b*line#) = x

96 - using the second method but accounting for the missing lines in the sequence

I think there some other ways but the correct answer is simply 19.