Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , respectively and area of cross sections $3.0 \times 10^{-5} \mathrm{~m}^2$ and $4.5 \times 10^{-5} \mathrm{~m}^2$, respectively are stretched by the same magnitude under a given load. The ratio of the Young's modulus of $A$ to that of $B$ is x : 3. The value of $x$ is