Vector \( a\hat{i} + b\hat{j} + \hat{k} \) & \( 2\hat{i} - 3\hat{j} + 4\hat{k} \) are perpendicular to each other when \( 3a + 2b = 7 \) the ratio of \( a \) to \( b \) is \( \frac{x}{2} \). The value of \( x \) is ______.