Dividing 2 texboxes to show result in 3rd textbox

Hi
I hope someone can help me with the issue i have
I am building up a new user form where i have few textboxes in which i can type in the values and i have another 2 textboxes where i receive result (Textbox 16 &17) with using the formula ( See below )
Now i need to divide them 2 texboxes and show the result in to textbox 15
I was trying to apply same statement which i used for getting the result to textbox 16 & 17 but its not working
I would be grateful if someone can help me to resolve this issue.

Dim dblTextBox2 As Double           'this will do the calculation for colour corrected values
Dim dblTextBox3 As Double
Dim dblTextBox4 As Double
Dim dblTextBox5 As Double
If TextBox2.Value <> "" Then dblTextBox2 = CDbl(TextBox2.Value)
If TextBox3.Value <> "" Then dblTextBox3 = CDbl(TextBox3.Value)
If TextBox4.Value <> "" Then dblTextBox4 = CDbl(TextBox4.Value)
If TextBox5.Value <> "" Then dblTextBox5 = CDbl(TextBox5.Value)
If dblTextBox2 > 0 And dblTextBox3 > 0 Then TextBox13.Value = Format(100 / 10 ^ (2 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox3 / 0.9216))), "0.0")
If dblTextBox2 > 0 And dblTextBox4 > 0 Then TextBox14.Value = Format(100 / 10 ^ (2 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox4 / 0.9216))), "0.0")
If dblTextBox2 > 0 And dblTextBox5 > 0 Then TextBox16.Value = Format(100 / 10 ^ (3.18 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox5 / 0.9216))), "0.0")
If dblTextBox2 > 0 And dblTextBox4 > 0 Then TextBox17.Value = Format(100 / 10 ^ (3.18 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox4 / 0.9216))), "0.0")
End Sub

Dim dblTextBox2 As Double           ' to valculate T550 (corrected)
Dim dblTextBox4 As Double
If TextBox2.Value <> "" Then dblTextBox2 = CDbl(TextBox2.Value)
If TextBox4.Value <> "" Then dblTextBox4 = CDbl(TextBox4.Value)
TextBox14.Value = 100 / 10 ^ (2 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox4 / 0.9216)))
If dblTextBox2 > 0 And dblTextBox4 > 0 Then TextBox14.Value = Format(100 / 10 ^ (2 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox4 / 0.9216))), "0.0")
If dblTextBox2 > 0 And dblTextBox4 > 0 Then TextBox17.Value = Format(100 / 10 ^ (3.18 / dblTextBox2 * WorksheetFunction.Log(100 / (dblTextBox4 / 0.9216))), "0.0")
End Sub