Answer
(a) root
(b) $k$
Work Step by Step
(a) If you divide $P(x)$ by $x-c$ and the remainder is $0$, then $c$ is a root of $P(x)$.
(b) The Remainder Theorem states that f $P(x)$ is divided by $x-c$, the remainder is equal to $P(c)$.
Thus, if $k$ is the remainder when $P(x)$ is divided by $x-c$, then $P(c)=k$.