Question 859468
You want to eliminate k.  Solve one equation for k, and substitute this into the other equation.


{{{k=n-ac}}} from second equation.
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{{{ab+c=k}}}
{{{ab+c=n-ac}}}
{{{ab+ac+c=n}}}
{{{ab+ac=n-c}}}
{{{a(b+c)=n-c}}}
{{{highlight(a=(n-c)/(b+c))}}}


Evaluate then, this expression according to the variable assignments:
{{{a=(6.5-0.25)/(0.75+0.25)}}}