The equation x + 3 = 7 is a simple algebraic expression where x represents an unknown value. To solve for x, you need to isolate it on one side of the equation. This is done by subtracting 3 from both sides, leading to x = 7 - 3. After performing the subtraction, you find that x = 4. This means that when you add 3 to 4, the result is 7. This equation is a basic example of how algebra helps in finding unknown values through simple operations.