Please fix your notation. You're all over the place on that on.

If you mean this: , you should have written 5^x = 4^(x+3). Parentheses make a difference.

This is okay, excepting the notation.

log [5^x] = log [4^(x+3)]

Again with notation confusion:

x log 5 = (x+3) log 4

Why are you stuck? Keep going!

x log 5 = x log(4) + 3 log 4

x log(5) - x log(4) = 3 log(4)

x [log(5) - log(4)] = 3 log(4)

Can you finish.

log(4) is a number. It may not be the prettiest number ever, but it's not the ugliest, either. Use it like any other number.