public OnPlayerKeyStateChange(playerid, oldkeys, newkeys)
{
  if(newkeys & KEY_FIRE)
  {
    if(IsPlayerInAnyVehicle(playerid))
    {
      new vehicleid = GetPlayerVehicleID(playerid);
      new Float:X,Float:Y,Float:Z;
      GetVehiclePos(vehicleid, X, Y, Z);
      SetVehiclePos(vehicleid, X, Y, Z +10);
    }
    return 1;
  }
  if(newkeys & KEY_HANDBRAKE)
  {
    if(IsPlayerInAnyVehicle(playerid))
    {
      new vehicleid = GetPlayerVehicleID(playerid);
      AddVehicleSpeed(vehicleid, 10.0)
    }
    return 1;
  }
  return 1;
}
stock AddVehicleSpeed(vid, Float:howmuch)
{
    static Float:T[3];
    GetVehicleVelocity(vid, T[0], T[1], T[2]);
    return SetVehicleVelocity(vid,T[0] * howmuch , T[1] * howmuch , T[2]);
}