Numeric Variables For Row & Column Numbers

I recorded a macro to perform a graphing operation which will be used in a For-Next Loop which will run eight times. I need to modify the “ range” portion of one of the recorded lines to allow the graphing data to be dependent on variables I have set up as integers. See the applicable part of the recorded code below.

Dim firstrowno As Integer
Dim ltcol As Integer
Dim lastrowno As Integer
Dim rtcol As Integer

‘code which sets the values of the above variables Is Not shown

ActiveChart.SetSourceData Source:= Sheets("PLOTS").Range("AN27:AQ33"), PlotBy _
:=xlColumns

How do I replace/modify the ("AN27:AQ33") in the code above using the variable integers; firstrowno, ltcol, lastrowno and rtcol ?