Question 838399
The {{{ 90 }}} fluid ounces that was added made
up the difference between {{{ 1/8 }}} full and {{{ 3/4 }}} full
Note that {{{ 3/4 = 6/8 }}}, and the difference {{{ 6/8 - 1/8 = 5/8 }}}
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This is saying that {{{ 5/8 }}} of the tank holds {{{ 90 }}} fluid ounces
Each of these {{{ 5 }}} 1/8's holds {{{ 1/5 }}} of {{{ 90 }}}
So {{{ 1/8 }}} of a tank holds {{{ 1/5 }}} of {{{ 90 }}}
{{{ 8 }}} times {{{ 1/8 }}} is a full tank, so 1 tank contains
{{{ ( 8/5 )*90 }}}
{{{ ( 8/5 )*90 = 720/5 }}}
{{{ 720/5 = 144 }}}
(a) 
The tank holds 144 fluid ounces
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(b)
Originally there was {{{ (1/8)*144 = 18 }}} fluid ounces
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(c) 
{{{ (2/3)*144 = 96 }}} fluid ounces
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Hope this helps