We can simplify the given equation as follows:
$$K\sqrt{28}+\sqrt{63}-\sqrt{7}=0$$
$$K\sqrt{4\cdot7}+\sqrt{9\cdot7}-\sqrt{7}=0$$
$$2K\sqrt{7}+3\sqrt{7}-\sqrt{7}=0$$
$$2K\sqrt{7}+2\sqrt{7}=0$$
$$2\sqrt{7}(K+1)=0$$
Since $\sqrt{7}$ is not zero, we can divide both sides by $2\sqrt{7}$ to get:
$$K+1=0$$
Therefore, $K=-1$.
So the answer is (B) -1.