Before you can deal with the log, you need to remove anything around it, like the 3 that's outside of it. So you do 6/3 which = 2 and you're left with log (x-4)=2. If there is no number in the base of the log, it's assumed to be 10 and we can undo logs by using exponents! So you do 10^2 which = 100. and 10^log(x-4) which undoes the log(10) so you're left with x-4=100.
Add 4 on both sides to get x =104. I hope this helped! If some parts don't make sense please ask!