plz help me solve 3,5, and 7 in desperate need of help ​

One expression below in undefined, and the other expression has a well defined value. which expression is undefined and explain why it has no value. which expression is defined? what is the value of that expression and how do you know? what is a different expression using a trig inverse function that is also undefined?

Because of your favorite lemonade it is $3.84 for 3 gallons. write this as an unit rate

1mile equals approximately 1.6 kilometers. which best approximates the number of miles in 6 kilometers?