Question 552325
<pre>
{{{matrix(4,1,

  9&5/9,    
  -6&5/6, 
  "----",
    ""  ) }}}

We can't subtract because they don't have the same 
denominator.  The LCD of 9 and 6 is 18, because 
both will divide evenly into 18. So we change {{{5/9}}}
to {{{10/18}}} and {{{5/6}}} to {{{15/18}}}

{{{matrix(4,3,

  9&5/9, ""="",  9&10/18,    
  -6&5/6, ""="",  6&15/18, 
  "----", ""  ,  "----" ,  
    ""  , ""  ,   ""    ) }}}

We still can't subtract because the upper fraction {{{10/18}}} 
has a smaller numerator than the lower fraction {{{15/18}}}.
So we borrow 1 from the 9, leaving it with 8, and that gives 
us {{{18/18}}} to add to the fraction {{{10/18}}} which just amounts 
to adding the denominator 18 to the numerator 10, getting 28, so 
we have this:

{{{matrix(4,5,

  9&5/9, ""="",  9&10/18, ""="", 8&28/18,   
  -6&5/6, ""="",  6&15/18, ""="", 6&15/18,
  "----", ""  ,  "----" ,  ""  , "----",
    ""  , ""  ,   ""    ,  ""  , "") }}} 

And now we can subtract because the numerator above is bigger
than the numerator below. So  8 minus 6 gives 2 for the whole part
of the answer, and 28-15 gives 13 for the numerator of the answer
so we subtract and get:

{{{matrix(4,5,

  9&5/9, ""="",  9&10/18, ""="", 8&28/18,   
  -6&5/6, ""="",  6&15/18, ""="", 6&15/18,
  "----", ""  ,  "----" ,  ""  , "----",
    ""  , ""  ,   ""    ,  ""  , 2&13/18) }}} 

Edwin</pre>