Igot a 20% on my first and 40% on my second try i really need getting this

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?

What is the fewest number of full weeks briyana would have to work to have enough money? 8 weeks9 weeks 10 weeks11 weeks

Apositive number a or the same number a increased by 50% and then decreased by 50% of the result?