Answer:
27 m/s
Explanation:
We can use constant acceleration kinematics, also known as SUVAT equations, to find the child's final speed. We will use an equation that is a function of initial speed (u), acceleration (a), time (t), and final speed (v).
v = u + at
v = (15 m/s) + (3.0 m/s²) (4.0 s)
v = 27 m/s