The given function is $f(x) = 6x + 8$, and the expression to evaluate is $f(9) - f(2)$.

Let's break it down:

1. Calculate $f(9)$: $f(9) = 6(9) + 8 = 54 + 8 = 62$

2. Calculate $f(2)$: $f(2) = 6(2) + 8 = 12 + 8 = 20$

3. Now, find the difference $f(9) - f(2)$: $f(9) - f(2) = 62 - 20 = 42$

Thus, $f(9) - f(2) = 42$.

Would you like further explanation or additional help?

Here are 5 related questions to explore:

1. How do you solve for $f(x)$ if the function is quadratic, like $f(x) = x^2 + 6x + 9$?
2. What happens when you are given a function with negative coefficients, like $f(x) = -3x + 5$?
3. How do you find $f(x)$ for an exponential function, such as $f(x) = 2^x$?
4. How would you calculate $f(a) - f(b)$ for arbitrary values of $a$ and $b$?
5. How does the slope of a linear function like $f(x) = 6x + 8$ relate to its graph?

Tip: When working with linear functions, always consider the slope-intercept form $y = mx + b$, where $m$ is the slope and $b$ is the y-intercept.