How do i solve the problem, when it says that i must be a interger
You probably need a subscript i on InterStorey_Deflection.
In general, you should upload a Mathcad file, rather than just an image, to make it easier to identify the problem.
I too agree that you should upload the Mathcad sheet, to allow us to help you better.
It seems that you missed to type an index i at the InterStorey_Deflection array, it should be: