Answer
$c=\frac{225}{4}$
Work Step by Step
Comparing $x^{2}-15x+c$ with $x^{2}+bx+c$, we see that $b=-15$.
The value of $c$ so that it completes the square is
$c=(\frac{b}{2})^{2}=(\frac{-15}{2})^{2}=\frac{225}{4}$.
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