Let focal length of convex lens is +$f$ then focal length of concave lens would be $-\frac{3}{2}f$.

From the given condition,

$\frac{1}{30}=\frac{1}{f}-\frac{2}{3f}=\frac{1}{3f}$

$\therefore f=10$ cm

Therefore, focal length of convex lens = + 10 cm and that of concave lens = -15 cm.