Using the laws of logs you can see that if you log both sides of the equation you get:
(2x+1)*log(8) = log(24)
Dividing both sides of the equation by log(8) you get:
2x+1 = log(24)/log(8)
Then it is a simple case of solving for x:
x = 0.5*(((log(24)/log(8))-1)
x = 0.264