Answer
$3(3x+2y)^2$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $27x^2+36xy+12y^2=\\=3(9x^2+12xy+4y^2)\\=3((3x)^2+2\cdot3x\cdot2y+(2y)^2)\\=3(3x+2y)^2$
