Given quantity is Q=c2a4b3.
The relative error in measuring Q is given by
QΔQ=4aΔa+3bΔb+2cΔc...(1)
Hence, the required percentage error is given by
\begin{matrix}\frac{\Delta Q}{Q}\times 100 & = & 4(\frac{\Delta a}{a}\times 100)+3(\frac{\Delta b}{b}\times 100)+2(\frac{\Delta c}{c}\times 100) \\ & = & 4\times 3%+3\times 4%+2\times 5% \\ & = & 12%+12%+10% \\ & = & 34%\end{matrix}