Question 136349
Not sure if you mean {{{6=(3/8)r }}} or {{{6=3/(8r)}}} 

If {{{6=(3/8)r }}}
{{{6 * (8/3) = r }}}
{{{16 = r }}}

If {{{6=3/(8r)}}} 
{{{8r = 3/6 }}}
{{{r = 3/(6*8) }}}
{{{r = 1/16}}}