To do the first question, simplify the equation, putting like terms together, by adding and subtracting to do this.
Then looking at the equation that you solved for, look and see if there are any other equations that are related in some way to the original solved equation.
Pay close attention to the positive and negative signs.
Answer:
Step-by-step explanation:
Key to this method is remembering that

So, if you divide the coefficient of x by 2 and square it, that will complete the square. With that in mind, things are easy.
6/2 = 3, so add 

So, c=9
Similarly, for the other two,

You don't really have to worry about the sign, since squaring will always make it positive

It’s B 20 students I am sure that’s correct