Hi, need some help on these questions:

16. Express logx in terms of log a, log b, and log c given that $\displaystyle x = a^2 \sqrt{b^3 c}$

20. $\displaystyle log_{a}2 = log_{b}16$, show that $\displaystyle b = a^4$

21. Find values of x for which:

a) $\displaystyle (log_{10}x)(log_{10}x^2) + log_{10}x^3 - 5 = 0$

b) $\displaystyle (log_{10}x)^2 - log_{10}x^2 +1 = 0$

c) $\displaystyle (log_{2}x^2)^2 - log_{2}x^3 - 10 = 0$

d) $\displaystyle (log_{3}x)^2 = log_{3}x^5 - 6$

Thanks a ton in advance!