Exercise 30 please , show work

Which of the following constants can be added to x2 - 3x to form a perfect square trinomial?

Margie is practicing for an upcoming tennis tournament. her first serve is good 20 out of 30 times on average. margie wants to know the estimated probability that her first serve will be good at least four of the next six times she serves. how could she design a simulation for this scenario?

Sole the equation 6n + 9 = -3n - 21 - 6 for n