Chapter 2 - Linear and Quadratic Functions - Section 2.1 Properties of Linear Functions and Linear Models - 2.1 Assess Your Understanding - Page 126: 3

$18$

The average rate of change from $2$ to $4$ is given by $\frac{f(4)-f(2)}{4-2}$. Thus, the average rate of change from $2$ to $4$ is: $\dfrac{f(4)-f(2)}{4-2}\\$ $=\dfrac{3(4)^2-2 -(3(2)^2-2)}{2}\\$ $=\dfrac{36}{2}=18$