To find the relative frequency, we need to first add up the total number of people in the age group 12-15 who had over 500 messages. From the table, we can see that there were 78 people aged 12-15 who had over 500 messages.
Next, we need to calculate the total number of people in the age group 12-15. From the table, we can see that there were a total of 24 + 47 + 78 = 149 people aged 12-15.
To find the relative frequency, we divide the number of people with over 500 messages by the total number of people in the age group 12-15:
Relative Frequency = (78/149) * 100
Relative Frequency = 52.3%
Therefore, the relative frequency of the people age 12-15 who had over 500 messages is 52.3% rounded to the nearest tenth.