I'm not sure that this is what you wanted, but the solution is x = 2500
[tex] log(4x) = 3 \\ rule > \: log_{a}(b) = x < = > \: b = {a}^{x} \\ 4x = {10}^{3} \\ 4x = 10 \: 000 \\ x = \frac{10 \: 000}{4} \\ x = 2500[/tex]
Note: when we have no number as the logarithmic base, it is 10 by default.
