A physical quantity $z$ depends on four observables $a, b, c$ and $d$, as $z=\frac{a^2 b^{\frac{2}{3}}}{\sqrt{c d^3}}$. The percentages of error in the measurement of $\mathrm{a}, \mathrm{b}, \mathrm{c}$ and d are $2 \%$, $1.5 \%, 4 \%$ and $2.5 \%$ respectively. The percentage of error in z is
