有一个题，一点头绪都木有，直接不知道是什么意思，求大神给指导指

Public Sub nJC(nSJ%) As Double
Dim i%
nJC = 1
If nSJ >= 2 Then
For i = 2 To nSJ
nJC = nJC * i
Next i
End If
End Sub
Private Sub 计算_Click()
Dim m%, n%, s#, cTS$
m = Val(InputBox("请输入 m（m >= 1）"))
n = Val(InputBox("请输入 n（n >= 1）"))
s = nJC(n) * nJC((m - n))
If Abs(s) < 1e-10 Then
cTS = "输入数据有错！"
Else
s = nJC(m) / s
cTS = "所求 s =" & Str(s)
End If
MsgBox cTS, 0 + 64, "计算结果"
End Sub