$64\,y^2 \,- 9 = $   ?

$(8y+9)(8y-9)$ $(8y+3)(8y-3)$ $(64y+3)(64y-3)$ $(8\,y^2+3)(8\,y^2-3)$

$9\,y^2 \,- 16 = $   ?

$(3\,y^2+4)(3\,y^2-4)$ $(3y+4)(3y-4)$ $(3y+4)^2$ $(9y+16)(9y-16)$

$16 \,- 16\,x^2 = $   ?

$(16+4x)(16-4x)$ $(4+4x)^2$ $(4+4\,x^2)(4-4\,x^2)$ $(4+4x)(4-4x)$

$25\,x^2 \,- 9 = $   ?

$(5x-3)^2$ $(25x+9)(25x-9)$ $(5x+3)(5x-3)$ $(5x+3)^2$