Question 66096
here we use the F.O.I.L. method where that stands for First Outside Inside Last. <br>

First -> 6r(6r)
Outside -> 6r(2x)
Inside -> -2x(6r)
Last -> -2x(2x)<br>

(6r - 2x)(6r + 2x)
= 6r(6r)+6r(2x)-2x(6r)-2x(2x)
= 36r^2+12rx-12rx-4x^2
= 36r^2-4x^2