Answer
$49$; $(x-7)^2$
Work Step by Step
To complete the square, add a term that is the square of half the coefficient of $x$ in the middle term. Then factor by trial and error.
$x^2-14x$
$(-\frac{14}{2})^2=7^2=49$
$x^2-14x+49$
$(x-7)^2$