It's always hard to read an image when it's sideways. Also (and you probably can't help this) the pages are curved in the image making things a bit skewed on that side. At the very least please put the image right side up. Even better would be to type it out.
What I can discern of the question posed in the displayed document seems to be a continuation of a series of previous scenarios,
and values that are required for this question seem to come from preceding paragraphs, that are not included.
Also you cannot assume that we will be instantly familiar with the symbology used in your text book, it may be different in other text books.
You have to provide sufficient context for us to be able to align your problem with our knowledge.