This makes no sense. To express logarithms of a certain base, please use language like
base 4 log of (3x-5) = 7
or
base 4 log(3x-5) = 7
or, if you want to be really slick
log4(3x-5) = 7
or
(Use "Show source" to see what I typed for these last two.)
Please repost your questions. (There are two other problems which look like this one and which were posted at about the same time so I suspect you posted them, too.)