Relative frequency = no. of successful outcomes / total no. of tries
In this case, 30/200 = 15/100 = 3/20
3/20 is the relative frequency, or relative probability, of rolling a 6. The accuracy of the relative frequency increases as you increase the number of times you roll the die. The theoretical probability of a 6 on a fair die is 1/6 = 10/60, whereas 3/20 = 9/60. Over 1000 rolls, or 2000, or even 10000, the relative probability should draw nearer to 1/6.