Simplify With For Loop VBA - excel

Question

So I am not very good with VBA and how it exactly how everything works but I am sure what I am doing can be condensed I am just not exactly sure how.
Here is the code I am working with:
Sub This()
If ComboBox5.Value = "Test" Then
If Range("R20").Value > 1 Then
Range("D37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[14]))+R[-17]C"
Range("E37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[13]))+R[-17]C"
Range("F37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[12]))+R[-17]C"
Range("G37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[11]))+R[-17]C"
Range("H37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[10]))+R[-17]C"
Range("I37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[9]))+R[-17]C"
Range("J37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[8]))+R[-17]C"
Range("K37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[7]))+R[-17]C"
Range("L37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[6]))+R[-17]C"
Range("M37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[5]))+R[-17]C"
Range("N37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[4]))+R[-17]C"
Range("O37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[3]))+R[-17]C"
Range("P37").Select
ActiveCell.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[2]))+R[-17]C"
End If
End If
I recorded this Macro, and it works fine, but if I want to do this as well for Range(R23) it is kind of pain. So how would I go about condensing this code. I am sure the formula is not very clear so I want the new updated value of D37 to be:
D37 = (|(R20 - 1)|*D20) + D20

Answer 1

Possibly something like this, though I try not to use R1C1 notation because it is so difficult to read, so I'm not sure this is exactly what you're looking for.
Sub This()
If ComboBox5.Value = "Test" Then
Dim rng as Range, cl as Range, i as Long
If Range("R20").Value > 1 Then
Set rng = Range("D37:P37")
rng.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C18))+R[-17]C"
End If
If Range("R23").Value > 1 Then
'## NOTE: You may need to modify if the Column changes
rng.FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C18))+R[-17]C"
Next
End Sub
Explanation of why I use C18 in the formula:
You're original code is using R1C1 notation with relative reference. As you traverse your range of cells (moving from left-to-right) your formula is decrementing the column position, e.g.:
Range("D37").FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[14]))+R[-17]C" '## C[14]
Range("E37").FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[13]))+R[-17]C" '## C[13]
So this means that even though you're changing the offset value in the brackets, you're still refering to the same column, which can be identified in absolute terms using R1C1 notation C18

Answer 2

It appears as though you are placing nearly the same formula in every column in the same row. So, as your title suggests, a for-loop might be appropriate. For instance,
For j = 4 to 100 'or whatever the last column number you want to be
cells(37, j).FormulaR1C1 = "=ABS(R[-17]C*(1-R[-17]C[" & 18 - j & "]))+R[-17]C"
next j