Suppose $\vec { \alpha }$ Is a Fixed Vector of Length 5

Essay

Suppose $\vec { \alpha }$ is a fixed vector of length 5, $\vec { b }$ is a vector which can rotate and has length 2, and $\theta$ is the angle between them.
What is the maximum value of $\vec { a } \cdot \vec { b }$ , and for what value of $\theta$ does it occur?