Chapter 2 - One-Dimensional Kinematics - Problems and Conceptual Exercises - Page 50: 42

$v_{i}=+7.44~m/s$

$a_{av}=\frac{\Delta v}{\Delta t}=\frac{v_{f}-v_{i}}{\Delta t}$. Rearrange the equation: $v_{f}-v_{i}=(a_{av})(\Delta t)$ $v_{i}=v_{f}-(a_{av})(\Delta t)$ $v_{i}=+9.31~m/s-(+6.24~m/s^{2})(0.300~s)$ $v_{i}=+7.44~m/s$