Question 902561
Let y = width.
Let h = the extra height beyond 25 cm to reach complete height.
First Part, unknown volume,  v = this unknown volume; {{{v=46*y*25}}}.


Second Part, known volume, 12000 cubic centimeters.
{{{45*y*(25+h)=12000}}}.


Not enough given information to find y.


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With a bit more work, 
{{{45*y*25+45*y*h=12000}}}
{{{45y(25+h)=12000}}}
{{{y=12000/(45(25+h))}}}
But still need more information for a value.