Macro variable help

Hello,

I have declared a variable

Dim x As String
x = Cells(x + 10, 10).Value

I am getting the value of a cell in x. I want to use that value in a sumif function which i have defined below

Cells(y,6).Formula = "=SUMIF(I25:I1000,& x &,F25:F1000)"

y is defined somewhere else so that is not a problem.

I keep getting a error here, how do i pass variable inside a sumif function.

Thanks for all your help