My score in math is a 69 pls help

Whats are the trickiest steps to do when adding or subtracting rational expressions? how does knowledge of rational numbers u in adding and subtracting rational expressions?

V=x^4-y^4 pick three expressions that can represent the three dimensions of the prism (each in meters)

Landon drove 103.5 miles on tuesday 320.75 miles on wednesday and 186.30 miles on thursday for work his company pays 0.07 $ for each mile he drives he expects to be paid more than $40,000 is he correct explain