Answer
Perfect square, $(k+6)^{2}$.
Work Step by Step
$k^{2}+12k+36=$
...write the last term as a square.
$=k^{2}+12k+(6)^{2}$
...does middle term equal $2ab$?
$12k=2\cdot(k)\cdot(6)$
$=k^{2}+2\cdot(k)\cdot(6)+(6)^{2}$
...write as the square of a binomial.
$=(k+6)^{2}$
Perfect square, $(k+6)^{2}$.
