The vapour pressure of \( A \) and \( B \) at \( 25^\circ \text{C} \) are \( 90 \, \text{mm Hg} \) and \( 15 \, \text{mm Hg} \) respectively. If \( A \) and \( B \) are mixed such that the mole fraction of \( A \) in the mixture is \( 0.6 \), then the mole fraction of \( B \) in the vapour phase is \( x \times 10^{-1} \). The value of \( x \) is __________. (Nearest integer)