<PRE><B>Question 366045</B>
{{{((-20+5z))/3}}}
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{{{((121z-484))/9}}}
:
Invert the dividing fraction and multiply
{{{((-20+5z))/3}}} * {{{9/((121z-484))}}}
:
look for common factors which will greatly simplify things here
{{{(5(-4+z))/3}}} * {{{9/(121(z-4))}}}
the same as:
{{{(5(z-4))/3}}} * {{{9/(121(z-4))}}}
:
You can cancel out: z-4, 3 into 9, leaving 
5 * {{{3/121}}} = {{{15/121}}}
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