Using Existing NORMSDIST() Function in VBA

My entire current function for my Black Scholes Calling Price Model is

Function BlackScholesCallOption(Stock As Double, Exercise As Double, Time As Double, Interest As Double, Sigma As Double)

Dim a As Single
Dim b As Single
Dim c As Single
Dim d1 As Single
Dim d2 As Single

a = Log(Stock / Exercise)
b = (Interest + 0.5 * Sigma ^ 2) * Time
c = Sigma * (Time ^ 0.5)
d1 = (a + b) / c
d2 = d1 - Sigma * (Time ^ 0.5)
BlackScholesCallOption = Stock * NormSDist(d1) - (Exercise * Exp(-Interest * Time)) * NormSDist(d2)
    
End Function

The only problem is that my NormSDist functions that i use in the second last line is not defined. I need help defining it so that it pulls from the excel function normsdist().

Thanks in Advance.