Given,
⇒log10 (r2spq3)⇒log10 pq3−log10 r2s⇒log10 (pq3)21−(log10 r2+log10 s)⇒21log10 pq3−(2log10 r+log10 s)⇒21(log10 p+log10 q3)−2log10 r−log10 s⇒21(log10 p+3log10 q)−2log10 r−log10 s
Hence, log10 (r2spq3)=21(log10 p+3log10 q)−2log10 r−log10 s.