18. Create the equation of a function whose rate of change is always negative, but is increasing as the value of x increases (as the graph moves left to right). Sketch a quick graph of the function, as well as stating it's equation.

The U.S. population can be modeled by the function y=165.6x¹.345, where y is in thousands and x is the number of years after 1800. (a) What was the population in 1970, according to this model? (b) is the graph of this function concave up or concave down? What does this mean? (c) Use numerical or graphical methods to find when the model estimates the population was 94,150,000. (a) According to the model, the population in 1970 was thousands. (Round to the nearest integer as needed.)

Extra Problem: A sprinter runs the 100-yard dash in 10 seconds in the following fashion. She starts at rest (0 velocity), and for the first 6 seconds she speeds up to her highest speed. Unable to maintain that speed, she is slowing down for the last 4 seconds. You are to sketch a graph of her position along the track (in yards) as a function of time (in seconds). Be aware that she does not turn around and run toward the starting line, and she runs through the finish line rather than coming to a stop at the finish line.

In 2011 online sales were $192 billion, and in 2015 they were $264 billion. (a) Find a linear function S that models these data, where S is the sales in billions of dollars and x is the year. Write S(x) in slope-intercept form. (b) Interpret the slope of the graph of S. (c) Determine when online sales were $246 billion. ..... (a) Write S(x) in slope-intercept form. S(x) = %3D (b) Interpret the slope of the graph of S. Choose the correct answer below. O A. Sales decreased by $18 billion in next 4 years. B. Sales decreased, on average, by $18 billion/yr. C. Sales increased, on average, by $18 billion/yr. D. Sales increased by $18 billion in next 4 years. (c) Online sales were $246 billion in the year