This question is something to do with radian measure. I've never studied this before (I understand a few of the formulas generally used with no idea how they are applied) and want to solve this question:
Two points P and Q lie on a circle with centre O. The radius of the circle is r cm and angle POQ = radians. The length of the arc PQ is 6 cm and the area of the sector PQ is .
Find the values of r and . 
Any help towards answering this is greatly appreciated.