Two wires A and B made of different materials of length 6.0 cm and 5.4 cm, respectively and area of cross sections 3.0 × 10–5 m2 and 4.5 × 10–5 m2, 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 ______ .