#### Answer

$36x^2-y^2$

#### Work Step by Step

Use special products to multiply the given expression, $
(6x+y)(6x-y)
.$
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the product of the expression above is
\begin{array}{l}\require{cancel}
(6x)^2-(y)^2
\\\\=
36x^2-y^2
.\end{array}