Help fast please

What number should be added to the expression x^2+3x+ in order to create a perfect square trinomial? 3/2 3 9/4 9

Will give brainliest for correct answer 8. use the distance time graph to answer these questions: a. what does the graph tell us about the velocity of the car? b. what is the average velocity of the car? (show work) c. is the velocity reflected in the graph positive or negative?d. is there any point on the graph where the car is not moving? how do we know?

What ratio is proportional to 18/21