(a) Given that \(\log_a x=p\) and \(\log_a y=q\), find, in terms of \(p\) and \(q\),

(i) \(\log_a axy^2\),

(ii) \(\log_a\left(\frac{x^3}{ay}\right)\),

(iii) \(\log_x a+\log_y a\).

(b) Using the substitution \(m=3^x\), or otherwise, solve

\(3^x-3^{1+2x}+4=0.\)