How do i solve this problem? how did they get 2.5?

Need ! give step by step solutions on how to solve number one \frac{9-2\sqrt{3} }{12+\sqrt{3} } number two x+4=\sqrt{13x-20} number three (domain and range) f(x)=2\sqrt[3]{x} +1

Find the equation of the trend line (line of best fit). show your work i'm using the points (34,76) (42,91)

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?