The quadratic expression uses the following formula:
![ax^2 + bx + c](https://img.qammunity.org/2019/formulas/mathematics/college/whqts6h18z10wthwlbd16oa4vh7do5c2sd.png)
The expression is missing the variable of c, and it is a perfect square trinomial.
To find c in a perfect square trinomial, we will use the following formula:
![c = ((b)/(2)})^2](https://img.qammunity.org/2019/formulas/mathematics/middle-school/cnwnwhox0quuo89oe5yb95zvsrohxcvrdg.png)
The value of b in this expression is 12. Plug this value into the formula:
![(12)/(2) = 6](https://img.qammunity.org/2019/formulas/mathematics/middle-school/twdrhp3gfe5uyfbtzle2h3vbx9cjverrnr.png)
![6^2 = \boxed{36}](https://img.qammunity.org/2019/formulas/mathematics/middle-school/grq7u1ftgiledk5xcaqs5os4wnx7pvxobv.png)
36 must be added to make this trinomial a perfect square.