User Defined Function

Hello all! I downloaded code to run the "bisection method" on a continuous function. However, it is hard coded for a specific equation. Is there any way that i can use a cell for a user to input his/her function f(x) = xxxxxx, then run the sub to iterate for the root?

Here is an example of how the function is hard coded (see bold at the bottom). This is a little user unfriendly, because the person using this would have to open VBE and manually change the function each time. I would like for the user to enter the function in a specific cell, and then run the sub. How can i pass the function input by a user into a cell to the sub? Thanks in advance!

Option Explicit
Dim a As Single, b As Single, c As Single
Dim k As Integer, Nmax As Integer
Dim epsilon As Single

Private Sub cmdAutomatic_Click()
    epsilon = Range("L16")
    Nmax = Range("L17")
    a = Range("b4")
    b = Range("c4")
    Range("d4").Value = f00(a)
    Range("e4").Value = f00(b)
    If f00(a) * f00(b) > 0 Then
        MsgBox ("For a = " & Str(a) & " and b = " & Str(b) & ", f(a)*f(b)>0." _
                & " Try new values of a and b.")
        Exit Sub
    End If
    
    c = 0.5 * (a + b)
    k = 0
    
    Do While Abs(f00(c)) > epsilon And k < Nmax
       Call cmdStep_Click
    Loop
End Sub

Private Sub cmdClear_Click()
    Dim i As Integer, j As Integer
    For i = 1 To 100
        For j = 2 To 8
            Cells(3 + i, j).Value = ""
            Cells(3 + i, j).Font.Bold = False
        Next j
    Next i
    Range("b4").Value = 0
    Range("c4").Value = 1
End Sub

Private Sub cmdStart_Click()
    a = Range("b4")
    b = Range("c4")
    Range("d4").Value = f00(a)
    Range("e4").Value = f00(b)
    If f00(a) * f00(b) > 0 Then
        MsgBox ("For a = " & Str(a) & " and b = " & Str(b) & ", f(a)*f(b)>0." _
                & " Try new values of a and b.")
    Else
        MsgBox ("Use button [Next Step] to iterate solution")
    End If
    k = 0
End Sub

Private Sub cmdStep_Click()
    k = k + 1
    c = 0.5 * (a + b)
    Cells(3 + k, 6).Value = c
    Cells(3 + k, 7).Value = f00(c)
    Cells(3 + k, 8).Value = f00(b) * f00(c)
    If f00(b) * f00(c) > 0 Then
        b = c
        Cells(4 + k, 3).Font.Bold = True
    Else
        a = c
        Cells(4 + k, 2).Font.Bold = True
    End If
    Cells(4 + k, 2) = a
    Cells(4 + k, 4) = f00(a)
    Cells(4 + k, 3) = b
    Cells(4 + k, 5) = f00(b)
    
End Sub

Private Function f00(x As Single) As Single
    f00 = x ^ 3 - 5 * x ^ 2 + 2 * x - 24
End Function