Question 1076651
{{{ x/b + y/b = 0 }}} —> {{{ x = -y }}}
Substitute for x in 2nd equation:
{{{ -y/a - y/b = 4 }}} —>  {{{  highlight(y = -4ab/(a+b)) }}}  —> {{{ highlight(x=4ab/(a+b)) }}}
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Check:

      {{{ x/b + y/b = 4a/(a+b) +  (-4a)/(a+b) = 0 }}}  (ok)
      {{{ x/a - y/b = 4b/(a+b) - (-4a/(a+b)) = 4(a+b)/(a+b) = 4 }}}  (ok)