Start by remembering that the square root symbol gives the non-negative root. The equation says that √(x + 3) is 9. To remove the square root, square both sides: x + 3 = 9² = 81. Now isolate x by moving the constant to the other side, so x = 81 - 3 = 78. Always check radical equations: substituting x = 78 makes the expression inside the root equal to 81, and √81 = 9. So the correct answer is 78.