Differentiation from first principles. please help! question is attached :)

Average salary for a medical assistant is $31,220 which is a 20% income tax bracket how much money would they pay in income tax?

Suppose a least-squares regression line is given by modifyingabove y with caret equals 4.302 x minus 3.293. what is the mean value of the response variable if xequals20?

The perimiter of a rectangle is 70 inches the legneth of the rectangle is 5 less than 3 times the width of the rectangle what is the width of the rectangle