Question 26935
It helps if you write your problem with parentheses, but I'll presume you're asking to solve for:
{{{(3/4)/(4/5)=(5/6)/x}}} This problem is best attacked by <b>cross multiplying</b> which is multiplying the numerator of one side of the equation by the denominator of the other and setting that equal to the product of the other denominator/numerator pair, e.g.:

If {{{a/b=c/d}}} then {{{ad=bc}}}

For your problem you would get:
{{{(3/4)x=(4/5)(5/6)}}} Multiplying fractions on the right gives:
{{{(3/4)x=(2/3)}}} Divide both sides by 3/4 (i.e. multiply both side by 4/3):
{{{(4/3)(3/4)x=(2/3)(4/3)}}} Solve
{{{x=8/9}}}