Select 'Single Player' then 'Arcade' from the first 2 menus then choose any event you want. For this achievement you must choose 'Gold' or 'Platinum' as the difficulty level from the choice of 'Steel', 'Bronze', 'Silver', 'Gold' and 'Platinum'. You have to win the Gold or Platinum medal TWICE for the SAME event, once with a bike and once with a car.