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

a. 1
b. 2
c. 4

When forming a perfect square trinomial you need to "complete the square".
All of the steps to completing the square when solving an equation:
1.  The leading coefficient must be 1.
2.  Divide b by 2.
3.  Square (b/2)
4.  Add (b/2)^2 to both sides to keep the polynomial balanced.
5.  You can now write the perfect square trinomial and solve.

x^2 - 3x
-3/2
(-3/2)^2 = 9/4 = 2 1/4
LETTER B

Yourself by using the internet

When i did the math i got 11 cm