Solver in a Loop for multiple rows by changing multiple columns

Hello guys.

I was having trouble running the Solver in multiple rows. However, I saw in this forum several threats that helped me evolve a lot using VBA (I'm starting my studies now in this language and solved the problem with Solver in a Loop).

I know it must be something simple that I'm missing, however, I cannot do that for two columns at a time (in this case, the P and the R columns).
Here are the spreadsheet and the code.
I would also like to add the R column.

Best Regards,
Gláuber.

Set Objective: $AI$12
To: Min
By Changing: $P$12;$R$12


Option Explicit

Sub LoopSolv()

Dim i As Integer

For i = 12 To Range("P" & Rows.count).End(xlUp).Row

If Cells(i, "P") <> "" Then
SolverReset
SolverOk SetCell:=Cells(i, "AI").Address, MaxMinVal:=2, ValueOf:=0, ByChange:=Cells(i, "P").Address, Engine:=1 _
, EngineDesc:="GRG Nonlinear"
 SolverAdd CellRef:=Cells(i, "AI").Address, Relation:=2, FormulaText:=Cells(i, "AI").Address
SolverSolve Userfinish:=True
End If

Next

End Sub