Something like this may be what you want.

Private Sub CommandButton3_Click()
'Enter something in D90 so D91 is used at 1st click
Dim iEnd As Integer
iEnd = 1 + Sheets(3).Range("D65536").End(xlUp).Row
Sheets(1).Range("A98").Value = "29 120"
Sheets(3).Range("D" & iEnd).Value = ComboBox1.Value
Sheets(3).Range("B" & iEnd).Value =
Application.WorksheetFunction.Sum(Sheets(1).Range( "C98:D98"))
Sheets(3).Range("C" & iEnd).Value =
Application.WorksheetFunction.Sum(Sheets(1).Range( "E98:F98"))
End Sub

However, I can only guess since your post is far from clear. Your 2nd
Sub seems to assume Joe and Bob could be a ComboBox1.Value. However,
the 1st Sub puts them in ComboBox4. Your post addresses handling user
input from only 1 of the 4 ComboBoxes. You don't need a CommandButton
to fill the ComboBoxes. You can do that in UserForm_Activate(). You
don't need 4 different loop variables to fill the ComboBoxes; 1 will
do. As my code implies, your references to sheets won't work. They
need to be, e.g., Sheets(3) or Sheets("Sheets3").

Hth,
Merjet