I really need assistance with this code for c++

I'm really confused by this problem and some help would be really appreciated.

Write a ­function named celsius get_celsius that accepts a Fahrenheit temperature as an argument and returns the temperature converted to Celsius. Demonstrate the function by ­calling it in a loop that displays a table of the Fahrenheit temperatures 0 through 20 and their Celsius equivalents.

#include <iostream>
#include <iomanip>
using namespace std;
/****** function prototypes *********/
//Place function prototypes here.


int main()
{
    double celsius;
    cout << "Temperature Conversion Table\n\n";
    cout << "Fahrenheit   Celsius\n"
        << "____________________\n";

    // Set output format
    cout << fixed << showpoint << setprecision(1);
    //This code creates a loop that starts the Fahrenheit variable at 0 
    //and continues as long as it is less than or equal to 20

    for (int fahrenheit = 0; fahrenheit <= 20; fahrenheit++)
    {
        //declare a variable called celsius. 
        celsius = (5 / 9) * fahrenheit - 32;
        //Make a call to the get_celsius function. 
        //Send in the fahrenheit variable as the argument to
        //the function call. 
        //Place value returned by the function into the celsius variable 
        //Print out the celsius variable with 1 place after the decimal
        //Use iomanip, setprecision, fixed, showpoint

    }

    return 0;
}

/*************************************************************
*                             get_celsius                         *
//Write out the get_celsius function. It takes in
//1 int parameter and returns a double value.
//The incoming parameter is a temperature value in Fahrenheit and
//the return value should be the Celsius equivalent of it.
* This function computes and returns the Celsius equivalent *
* of the Fahrenheit temperature passed to it. It does not print out the
* value in this function               *
*************************************************************/