i have two questions and i also have the answers to them, but i dont know how they gotten them. can someone please explain it step by step?

1. the productivity of a person at work (on a scale of 0 to 10) is modelled by a cosine function: 5cos((pi)t/2) + 5, where t is in hours. If the person starts work at t=0, being 8:00 am, what times is the worker the least productive?

answer: 10a.m. and 2.pm.

2.At t=0 a car is due 2km north of you heading west moving 13km/s after 1.5s. what is the angle in radians between you and the car from where the car was at t=0

answer: 1.469radians

i appreciate the help ! (: