Question 904339
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To substitute the given values early,
{{{highlight_green((50*25+x*70)/(x+50)=45)}}}
Just be careful with the arithmetic and the decimal usage, and you should have no real trouble.


{{{(50*25+x*70)/(x+50)=45}}}


{{{(10*25+14*x)/(x+50)=9}}}


{{{14x+250=9(x+50)}}}


{{{14x+250=9x+450}}}


{{{5x=200}}}


{{{x=200/5}}}


{{{highlight(x=40)}}}, this number of mL



Does that work?
{{{(50*25+40*70)/(40+50)=45}}}
Yes.