Convert the logarithmic equation into exponential form. The statement log_10(x + 1) = 5 means x + 1 = 10^5. Now calculate 10^5 = 100000, so x + 1 = 100000. Subtract 1 from both sides: x = 100000 - 1 = 99999. Finally, check the domain: x + 1 must be positive, and 99999 + 1 = 100000 > 0, so the answer is valid.