We have the equation:
let's write in the standard form to identify the values of the constants:
from this we notice that a=1, b=-12 and c=36. Plugging this values into the discriminant we have:
Since the discriminant is equal to zero that means that the equation has only one solution of multiplicity 2.
Let's find the solution with the general formula; plugging the values of a, b and c we have:
Therefore the solution of the equation is 6.