This will put the formula in G with code and then replace with values- not sure I follow what else you want to do.
With Range("F2", Range("F" & Rows.Count).End(xlUp)).Offset(, 1)
    .Formula = "=IF(COUNTA(A2:B2)=0,0,IF(F2=""CAN"",20,IF(OR(F2=""FAS"",F2=""FAR""),10)))"
    .Value = .Value
End With