Salut,
[tex]log_{30}16=log_{30}2^4=4\cdot log_{30}2=4\cdot log_{30}\dfrac{30}{15}=4(log_{30}30-log_{30}15)=\\\\=4[1-log_{30}(3\cdot 5)]=4(1-log_{30}3-log_{30}5)=4(1-a-b).[/tex]
Green eyes.
