Question 330467
{{{81s^6-3f^6}}}
{{{3*(27s^6 - f^6)}}}  use difference of two cubes (http://www.purplemath.com/modules/specfact2.htm)

Then look here for the answer
http://www.wolframalpha.com/input/?i=81s^6-3x^6

Here is another website that is good for factoring
http://72.3.253.76:8080/webMathematica3/quickmath/page.jsp?s1=algebra&s2=factor&s3=basic

Hope this helps