If the relative frequency of a six is 0.2 , then here are two conclusions that can be drawn:
1). In 200 throws, you can expect to see a 'six' (200 x 0.2) = 40 times.
2). That cube is not honest, and you should not participate in a game where it's used. The relative frequency of any number ... 1, 2, 3, 4, 5, or 6 ... should be 0.1666... . That particular cube is coming up '6' about 20% more often than it should.
To work this out you need to multiply the probability, 0.2 by 200, the amount of throws, this will equal 40, but remember this is only an estimate and in reality it can differ just by chance. I hope that helped.