Self explanatory really but if you're looking for a very quick way to get this then ONCE THE CAMPAIGN is completed just simply replay the final stage(27). Just spam A when gripping up and let the rider get bucked off after about 3 seconds,repeat for all 6 bulls,this will take approx 3 minutes resulting in 600k which will enable you to buy 30 bronze booster packs. You should have open around 80/90 during the campaign alone so simply repeat this process 5/6 times.