log(x+9) = log x + log 9
Since log(a) + log(b) = log(ab),
log(x+9) = log (x*9)
Rewrite the x*9 as 9x:
log (x+9) = log (9x)
Raise 10 to both sides, which is the inverse of the log function, resulting in:
x+9 = 9x
Subtract x from both sides:
9 = 8x
Divide both sides by 8:
x = 9/8
Check:
log ((9/8) + 9) = log (9/8) + log 9
log (81/8) = log ((9/8)(9)) = log (81/8)