Add two columns value in ASP.Net RDLC expression

When i add using the above function i get 87 which is wrote where i add 8 plus 9 it gives me 87.

When i try to add these values after conversion i don't get the right figure.

=IIF((Fields!maths1.Value) > 0,Code.Grading(Fields!maths1.Value),"")+IIF((Fields!scen1.Value) > 0,Code.Grading(Fields!scen1.Value),"")