Answer
$(x-6-7y)(x-6+7y)$
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: $x^2-12x+36-49y^2=\\=x^2-2\cdot x\cdot6+6^2-(7y)^2\\=(x-6)^2-(7y)^2\\=(x-6-7y)(x-6+7y)$