Consider the system $$\left\{\begin{aligned}
x+2 y+6 z &=5 \\
-3 x-6 y+5 z &=8 \\
2 x+6 y+9 z &=7
\end{aligned}\right.$$ a. Verify that $x=-1, y=0, z=1$ is a solution of the system.
b. Find the determinant of the coefficient matrix.
c. Without solving the system, determine whether there are any other tions.
d. Can Cramer's Rule be used to solve this system? Why or why not?