Distance Between Centers of Tangent Circles at an Angle

Two circles are tangent to the same line from opposite sides. The line connecting their centres intersects the tangent line at an angle of $30^\circ$.
Calculate the distance between the centres of the circles given the following radii:
a) $2 \, \text{cm}$ and $5 \, \text{cm}$
b) $3 \, \text{cm}$ and $6 \, \text{cm}$