Question 733592
Let {{{ x }}} = the radiator's capacity in quarts
After losing mixture, {{{ 9 }}} quarts of water filled the radiator,
so {{{ 9 }}} quarts of mixture was lost
-------------
You started with {{{ .25x }}} quarts of antifreeze and lost 
{{{ .25*9 = 2.25 }}} quarts, so there is {{{ .25x - 2.25 }}} quarts
of antifreeze in the radiator before the water is added
-------------
{{{ ( .25x - 2.25 ) / x = .12 }}}
{{{ .25x - 2.25 = .12x }}}
{{{ .13x = 2.25 }}}
{{{ x = 17.3077 }}}
The capacity of the radiator is 17.3077 quarts
check answer:
There is {{{ .25*17.3077 = 4.327 }}} quarts of antifreeze to start
{{{ .25*9 = 2.25 }}} quarts of antifreeze were lost
{{{ 4.327 - 2.25 = 2.077 }}} quarts of antifreeze left
After water is added, 
{{{ 2.077 / 17.3077 = .120004 }}}
close enough
Hope I got it