The Crew - Ghost Bustin - Beat any Platinum Skill Ghost. [Bronze / 10G]

Platinum skill ghosts (and platinum medals) become available when reaching level 50. You can level up very quickly by completing story missions and repeating skill challenges.
Once you are level 50 you must select a skill challenge on your map and click on Ghost select. Here you need to change the ghost from gold to platinum. The jump skills are the easiest to do. It doesn't matter what car you use for this.