1. Solve the system of equations: $$ \begin{cases} 7x - 9y = 16 \\ -21x + 27y = -24 \end{cases} $$
2. Solve the system of equations: $$ \begin{cases} 4x + 3y = 2 \\ 20x + 15y = 10 \end{cases} $$
3. Solve the system of equations: $$ \begin{cases} x - 4y = -1 \\ -3x + 12y = 3 \end{cases} $$
4. Solve the system of equations: $$ \begin{cases} -11x + 12y = 60 \\ -22x + 24y = 90 \end{cases} $$
5. Solve the system of equations: $$ \begin{cases} 2x + 4y = 7 \\ y = -\frac{1}{2}x - 4 \end{cases} $$
6. Solve the system of equations: $$ \begin{cases} -3x - y = 8 \\ 6x + 2y = -16 \end{cases} $$
7. Solve the system of equations: $$ \begin{cases} 5x - 8y = 12 \\ 10x - 16y = 20 \end{cases} $$
8. Solve the system of equations: $$ \begin{cases} 2x + y = 3 \\ 6x + 3y = 9 \end{cases} $$
9. Solve the system of equations: $$ \begin{cases} 3x + 2y = 6 \\ -6x - 4y = -12 \end{cases} $$
10. Solve the system of equations by substitution: $y = 3x + 1$ and $6x - 2y = -2$. What is the solution?