Return only numbers directly after specific substring

With a UDF

Function NumAftRX(rData As Range) As Double
Dim item As String, st As Integer, num As Long
item = rData.Value
st = InStr(item, "RX") + 2
For x = st To Len(item)
    If IsNumeric(Mid(item, x, 1)) Then num = num & Mid(item, x, 1)
Next
NumAftRX = num
End Function

Kind regards
Leo