1. **Problem:** Solve the equation $2x + 3 = 7$. 2. **Formula and Trick:** To solve linear equations like this, use the trick "undo operations in reverse order". Start by undoing addition or subtraction, then undo multiplication or division. 3. **Step-by-step solution:** - Start with $2x + 3 = 7$ - Undo the addition of 3 by subtracting 3 from both sides: $2x + 3 - 3 = 7 - 3$ - Simplify: $2x = 4$ - Undo the multiplication by 2 by dividing both sides by 2: $\frac{2x}{2} = \frac{4}{2}$ - Simplify: $x = 2$ 4. **Explanation:** We reversed the operations done to $x$ to isolate it. First, we removed the added 3, then divided by 2 to get $x$ alone. 5. **Final answer:** $x = 2$