Question 152478
I'm assuminng you mean like this,
{{{((6-3x)/5)/((4x-8)/25)}}}
Dividing by a fraction is like multiplying by the reciprocal of the fraction. 
So
{{{(A/B)/(C/D)=(A/B)*(D/C)}}}
So in your case,
{{{((6-3x)/5)/((4x-8)/25)=((6-3x)/5)*(25/(4x-8))}}}
{{{((6-3x)/5)/((4x-8)/25)=((6-3x)/cross(5))*(cross(25)5/(4x-8))}}}
{{{((6-3x)/5)/((4x-8)/25)=(3(2-x))*(5/(4(x-2)))}}}
{{{((6-3x)/5)/((4x-8)/25)=(-3(x-2))*(5/(4(x-2)))}}}
{{{((6-3x)/5)/((4x-8)/25)=(-3*cross((x-2)))*(5/(4*cross((x-2))))}}}
{{{((6-3x)/5)/((4x-8)/25)=(-3)*(5/4)}}}
{{{((6-3x)/5)/((4x-8)/25)=-15/4}}}