##x = 5/8##
You used Logarithm of a product (based on the symbol you used which is addition).
##log2 + log(4x-1) = 3##
##log 2(4x-1) = 3##
##log (8x-2) = 3##
##8x-2 = 3##
##8x = 3+2##
##8x = 5##
(then divide them with 8 so that we can remove the value of x which is not applicable) so..
##8x-:8 = 5-:8##
##x = 5/8##