LNK2019 how to solve in the case? Everything seems to be correct

I have that common LNK2019 error and can not figure out what is wrong.

Here is my Solution Explorer:

Here is my Rectangle.cpp:

class Rectangle
{
    public:
        int getArea()
        {
            return this->width*this->height;
        }
        int width;
        int height;
};

Here is my Rectangle.h:

#pragma once
class Rectangle
{
    public:
        int getArea();
        int width;
        int height;
};

Here is my Functions.cpp:

#include <iostream>
#include "Rectangle.h";

using namespace std;

int main()
{
    Rectangle r3{ 2, 3 };
    cout << r3.getArea();

    return 0;
}

I am very new to C++ and it seems I did everything correctly, but still I am getting an error.