Question 41028
Try this:

{{{1/n - 1/3n = 1/6}}} Simplify.
{{{(3-1)/3n = 1/6}}}
{{{2/3n = 1/6}}} Multiply both sides by 3n.
{{{2 = 3n/6}}} Multiply both sides by 6.
{{{12 = 3n}}} Finally, divide both sides by 3.
{{{n = 4}}}

Check:
{{{1/4 - 1/(3*4) = 1/6}}}
{{{1/4 - 1/12 = 1/6}}}
{{{3/12 - 1/12 = 1/6}}}
{{{2/12 = 1/6}}}
{{{1/6 = 1/6}}}