c++ - What is the correct method for class import in multiple project solution

The solution consists of a Main project containing a main.cpp file and a separate Shape project consisting of a Shape.h and Shape.cpp.

When I define a class function inline in the header file and reference it in the main file the code executes, however defining it in a separate .cpp file results in LNK1120 and LNK2019 errors.

The folder structure is as follows:

+-- MainProj
|   +-- main.cpp
+-- Shape
|   +-- Shape.h
|   +-- Shape.cpp

I have tried adding the path containing Shape.cpp to includes directory but the issue persists.

main.cpp

#include 
#include "Shape/Shape.h"

using namespace std;

void main()
{

    Shape s(2, 3);
    cout << s.Area() << endl;
}

The following code works.
Shape.h

#pragma once
class Shape

{
public:
    Shape(float l, float w) : length(l), width(w)
    {
    }

    float Area()
    {
        return length * width;
    }

protected:
    float length;
    float width;
};

The following code results in the link errors below.
Shape.h

#pragma once

class Shape
{
public:
    Shape(float l, float w);
    float Area();
protected:
    float length;
    float width;
};

Shape.cpp

#include "Shape.h"

Shape::Shape(float l, float w) : length(l), width(w)
{
}
float Shape::Area()
{

    return length * width;
}

Severity Code Description Project File Line Suppression State
Error LNK1120 2 unresolved externals Main C:\CPP\Main\x64\Debug\Main.exe 1

Severity Code Description Project File Line Suppression State
Error LNK2019 unresolved external symbol "public: float __cdecl Shape::Area(void)" (?Area@Shape@@QEAAMXZ) referenced in function main MainProj C:\CPP\MainProj\main.obj 1

Severity Code Description Project File Line Suppression State
Error LNK2019 unresolved external symbol "public: __cdecl Shape::Shape(float,float)" (??0Shape@@QEAA@MM@Z) referenced in function main MainProj C:\CPP\MainProj\main.obj 1