1. Problem: Find the first quartile (Q1) of the data set: 21, 35, 17, 43, 8, 59, 72, 119. 2. Formula and rules: The first quartile Q1 is the value below which 25% of the data fall. To find Q1, first sort the data in ascending order, then find the position using $$Q1 = \frac{1}{4}(n+1)$$ where $n$ is the number of data points. 3. Sort the data: 8, 17, 21, 35, 43, 59, 72, 119. 4. Number of data points $n=8$. 5. Calculate position of Q1: $$Q1 = \frac{1}{4}(8+1) = \frac{9}{4} = 2.25$$. 6. This means Q1 lies between the 2nd and 3rd data points. 7. Interpolate between 2nd (17) and 3rd (21) data points: $$Q1 = 17 + 0.25 \times (21 - 17) = 17 + 1 = 18$$. 8. Final answer: The first quartile of the data set is $18$.