Question: Solve the system: {2x + y = 7; x - y = 2}
1. **State the problem:** We need to solve the system of linear equations:
$$\begin{cases} 2x + y = 7 \\ x - y = 2 \end{cases}$$
2. **Formula and rules:** To solve a system of linear equations, we can use substitution or elimination. Here, we'll use substitution.
3. **Isolate a variable:** From the second equation, isolate $x$:
$$x = y + 2$$
4. **Substitute:** Substitute $x = y + 2$ into the first equation:
$$2(y + 2) + y = 7$$
5. **Simplify:**
$$2y + 4 + y = 7$$
$$3y + 4 = 7$$
6. **Solve for $y$:**
$$3y = 7 - 4$$
$$3y = 3$$
$$y = \frac{3}{3}$$
$$y = 1$$
7. **Substitute back to find $x$:**
$$x = y + 2 = 1 + 2 = 3$$
8. **Solution:** The solution to the system is:
$$\boxed{(x, y) = (3, 1)}$$