The range in statistics is given as the difference between the lowest observed value and the highest observed value.
From the data provided, the highest observed value is 19, and the range is 8, then we have;
The value of m is 11
If the range is 8, then it simply means, you have deducted an unknown number (which is the lowest) from 19 to arrive at 8. Working backwards, that number is 11.