Question: Find the value of $x$.
1. **State the problem:** We need to find the value of $x$ from the given context.
2. **Analyze the information:** The user mentions font sizes increasing by 2 at intervals 0, 5, 10, 15, 20 and then mentions $x$ and 129 hours and miles, but no explicit equation is given.
3. **Assumption:** Since the problem is unclear, we assume a linear relationship where font size increases by 2 units every 5 units of time or distance.
4. **Set up the equation:** If font size at 0 is baseline, then at $x$ units, font size is $129$.
5. **Calculate $x$:** Since font size increases by 2 every 5 units, the increase from 0 to $x$ is $129$ units.
$$\text{Number of increments} = \frac{129}{2} = 64.5$$
Each increment corresponds to 5 units, so
$$x = 64.5 \times 5 = 322.5$$
6. **Conclusion:** The value of $x$ is $322.5$ units.
**Final answer:** $x = 322.5$