From Förberedande kurs i matematik 1

Exactly as in exercise c, we write the left-hand side as \displaystyle \text{1}0^{-x}, and the right-hand side as \displaystyle 0.000\text{1}=\text{1}0^{-4}, i.e. \displaystyle \text{1}0^{-x}=\text{1}0^{-4}, which gives \displaystyle x=\text{4}.