Question 620728
{{{x/3y=4/7}}}
{{{z/5y=2/21}}}
{{{x/z="?"}}}


{{{x/3y=4/7}}}
{{{x=4(3y)/7}}}
{{{x=12y/7}}}.............(1)



{{{z/5y=2/21}}} 
{{{z=(5y)2/21}}}
{{{z=10y/21}}}..............(1)
Divide x by z, we have
{{{x/z=(12y/7)/(10y/21)}}}
{{{x/z=(12y/7)(21/10y)}}}
{{{x/z=(cross(12y)/cross(7))(cross(21)/cross(10y))}}}
{{{x/z=(6/1)(3/5)}}} 
{{{x/z=18/5}}}
{{{x/z=3&3/5}}}