Decoupling: Unable to implement indirect referencing - vb.net

Question

There are three parts to my code A, B, C. B is a class library which references A which is also a class library. In A, a class MathOperations is defined which contains a function ADD. The part B has a class Factory which in-turn has a function createMathsObject which returns an object of MathOperations type. The part C refers to B. I can do away with part B and create the object of MathOperations type in part C and make C reference A directly where that class is defined. However I am trying to see how I can de-couple sections of the code, in this case A and C.I give the code for each of the three parts A, B and C. The error message that I get is mentioned later for which I need your help.
Part A: Class Library - Named as MathLibrary.dll
Public Class MathOperations
Function ADD(ByVal a As Integer, ByVal b As Integer) As Integer
Return (a + b)
End Function
End Class
Part B: Class Library - Named as FactoryMathsLibrary.dll which references MathLibrary.dll
Imports MathLibrary
Public Class Factory
Shared Function createMathsObject() As MathOperations
Return New MathOperations()
End Function
End Class
Part C: Exe file - which references FactoryMathsLibrary.dll
Imports FactoryMathsLibrary
Module Module1
Sub Main()
Dim a, b As Integer
Dim m As Object = Factory.createMathsObject() 'Error comes here
Console.Write("Enter 1st value: ")
a = Console.ReadLine()
Console.Write("Enter 2nd value: ")
b = Console.ReadLine()
Console.WriteLine("a + b = {0}", m.ADD(a, b))
Console.ReadLine()
End Sub
End Module
I was under the impression that since C references B and B references A, everything would be fine. But I am getting an error in the line Dim m As Object = Factory.createMathsObject(). The error message is as follows: Can someone pls help with the reason behind the error and the solution??

Answer 1

I did exactly what you did, in your exe-project you haven't added reference to "MathLibrary.dll". You can't include a library that references to another library without including that second library in your exe-project too (Unless you merge them into one)! if you won't include it too, you will have exactly the issue that you are having.
And so, you only have to add reference to "FactoryMathsLibrary.dll" and to "MathLibrary.dll"
Project > project_name Properties... > References > Add... > MathLibrary.dll > OK
❌ Without reference
✔️ With reference