C / C++ / MFC

class Employee
{

public:
	Employee(char* name, int hourFee, int hoursPerMonth, int overTime);
	Employee(char* name, int hourFee, int hoursPerMonth);
	Employee(char* name, int hourFee);

	static int _minimumFee;
	static int _maximumHours;

	int getSalary();
	void print();
	int getHourFee();
	void setHourFee(int hourFee);
	int gethoursPerMonth();
	void setHoursPerMonth(int hours);

private:

	char* _name;
	int _hourFee;
	int _hoursPerMonth;
	int _overTime;
};

#include"Employee.h"
#include<stdio.h>
#include<iostream>
#include<string.h>

using namespace std;

Employee::Employee(char* name, int hourFee, int hoursPerMonth, int overTime)
{
	_name = strdup(name);
	_hourFee = hourFee;
	_hoursPerMonth = hoursPerMonth;
	_overTime = overTime;
	Employee::_minimumFee = 3600;
	Employee::_maximumHours= 190;
}
Employee::Employee(char* name, int hourFee, int hoursPerMonth)
{
	Employee::Employee(name, hourFee, hoursPerMonth, 0);
}
Employee::Employee(char* name, int hourFee)
{
	Employee::Employee(name, hourFee, 160, 0);
}

int Employee::getSalary()
{
	return (_hourFee * _hoursPerMonth) + (_overTime * (_hourFee * 2));
}
void Employee::print()
{
	cout << "Employee, " << _name << " Salary = " << getSalary() << " hour Fee = " << _hourFee
		<< " hours of work per month " << _hoursPerMonth << " over hours made = " << _overTime << endl;
}

void Employee::setHourFee(int hourFee)
{
	if (hourFee < Employee::_minimumFee)
	{
		cout << "can't underpay a worker!!!" << endl;
		return;
	}
	else
	{
		_hourFee = hourFee;
	}
}
int Employee::getHourFee()
{
	return _hourFee;
}

int Employee::gethoursPerMonth()
{
	return _hoursPerMonth;
}


void Employee::setHoursPerMonth(int hours)
{
	if(hours > Employee::_maximumHours)
	{
		_hoursPerMonth = 190;
		_overTime = (hours - _hoursPerMonth);
	}
	else
	{
		_hoursPerMonth = hours;
	}
}

Error	3	error LNK2019: unresolved external symbol "public: static int Employee::_minimumFee" (?_minimumFee@Employee@@2HA) referenced in function "public: __thiscall Employee::Employee(char *,int,int,int)" (??0Employee@@QAE@PADHHH@Z)	Employee.obj	<br />