[GTLS]

First, have some global variables.

PHP код:

 new PlayerBet[MAX_PLAYERS];
new RaceWinner; 


Set that value to -1 Under OnPlayerConnect to you know, reset the variable.

PHP код:

 PlayerBet[playerid] = -1; 


then, inside /bet command, set PlayerBet[playerid] to the a playerid he put the bet on.
after that when a player finishes the race, make it automatically by entering the CP or something or manually by using, /setwinner for admins.

Then, using a loop, just check what player had win.

PHP код:

new pCount;
foreach(new i : Player)
{
      if(PlayerBet[i] >= 0)
           pcount++;
}

for(new i = 0;i<pCount;i++)
{
         if(PlayerBet[i] == RaceWinner)
           {
                   SCM(i, -1, "You won the bet!");
                   GivePlayerMoney(i,5000); //You can give em money or something.
            }
          else if(PlayerBet[i] == -1) continue; //People who didnt placed bet.
           else SCM(i, -1, "Sorry you lost the bet.");
        
           PlayerBet[i] = -1; //We gotta reset the variable, making it ready for next race, right!!
} 


Well, thats the rough idea of how to do it.. I hope you get the idea.. if some problem comes, you can ask again.