Find the percent decrease from 30 to 21

Plz need answer now will mark which situations represent linear functions? check all that apply. a)the temperature rises and falls over the course of a day. temperature is a function of time. b)a baseball is hit into the outfield. the height of the ball is a function of time. c)a car goes 55 mph on the highway. distance is a function of time. d)a child grew 2 inches this year and 1 inch last year. height is a function of time. e)a movie director makes 2 movies per year. the number of movies is a function of the years.

Solve the system of equations. y= 2x y= x^2 - 15

The base of a triangle exceeds the height by 9 inches. if the area is 180 square inches, find the length of the base and the height of the triangle.