Hi Anil,
You can use the INCLUDE STRUCTURE to add another QTY Field like QTY_NEW in your existing Structure with required data type (as per your final result, after calculation).
Since you are doing CORRESPONDING FIELD query, so it will work.
And while doing Calculation, update the QTY Information in QTY_NEW field.
And use that field in you BSC coding.
ASSIGN COMPONENT 'QTY' OF STRUCTURE <fs_gwa_tab> to <lw_amnt>.
ASSIGN COMPONENT 'QTY_NEW' OF STRUCTURE <fs_gwa_tab> to <val>.
<val> = <lw_amnt> * 100.
reagrds.
Praveer.