Question: Solve the system by the substitution method.
$x + 2y = 6$
$y = 2x + 3$
1. **State the problem:** Solve the system of equations using the substitution method:
$$x + 2y = 6$$
$$y = 2x + 3$$
2. **Substitution method formula:** Substitute the expression for $y$ from the second equation into the first equation.
3. **Substitute $y = 2x + 3$ into $x + 2y = 6$: **
$$x + 2(2x + 3) = 6$$
4. **Simplify the equation:**
$$x + 4x + 6 = 6$$
$$5x + 6 = 6$$
5. **Isolate $x$: **
$$5x + 6 - 6 = 6 - 6$$
$$5x = 0$$
$$\cancel{5}x = \cancel{0}$$
$$x = 0$$
6. **Find $y$ by substituting $x=0$ into $y = 2x + 3$: **
$$y = 2(0) + 3 = 3$$
7. **Solution:** The solution to the system is the ordered pair:
$$(0, 3)$$
8. **Check:** Substitute $x=0$ and $y=3$ into the first equation:
$$0 + 2(3) = 6$$
$$6 = 6$$ which is true.
Therefore, the system has a unique solution $(0, 3)$.
**Answer:** A. The solution is $(0, 3)$.