19.1 Hope this helps a lot
Answer:
.
Step-by-step explanation:
The given expression is

It can be rewritten as

![[\because \cos^{-1}(-x)=\pi-\cos^{-1}(x), x\in [-1,1]]](https://tex.z-dn.net/?f=%5B%5Cbecause%20%5Ccos%5E%7B-1%7D%28-x%29%3D%5Cpi-%5Ccos%5E%7B-1%7D%28x%29%2C%20x%5Cin%20%5B-1%2C1%5D%5D)
![2\left [\pi-\cos^{-1}\left(\cos \frac{\pi}{4}\right)\right]](https://tex.z-dn.net/?f=2%5Cleft%20%5B%5Cpi-%5Ccos%5E%7B-1%7D%5Cleft%28%5Ccos%20%5Cfrac%7B%5Cpi%7D%7B4%7D%5Cright%29%5Cright%5D)
![2\left [\pi-\frac{\pi}{4}\right]](https://tex.z-dn.net/?f=2%5Cleft%20%5B%5Cpi-%5Cfrac%7B%5Cpi%7D%7B4%7D%5Cright%5D)
![2\left [\frac{4\pi-\pi}{4}\right]](https://tex.z-dn.net/?f=2%5Cleft%20%5B%5Cfrac%7B4%5Cpi-%5Cpi%7D%7B4%7D%5Cright%5D)

Hence, the exact value of given expression is
.
The statement which is true in the choices is the third item in the choices such as "Nina makes 20x dollars at the clothing store each week". It was clearly stated in the given that x represent the total number of hours she worked in a week. This statement made the other items in the choices wrong.