We may use the change of base method (https://en.wikipedia.org/wiki/Logarithm#Change_of_base) and write
lnx=logex=log10xlog10e=log10x⋅1log10e\ln x = \log_{e}x = \dfrac{\log_{10}x}{\log_{10}e} = \log_{10}x\cdot \dfrac{1}{\log_{10}e}lnx=logex=log10elog10x=log10x⋅log10e1 ,
the second multiplier is a constant, so we expressed the natural logarithm as a common logarithm multiplied by a constant.