I've been trying to figure where to start with this, but no luck. I hope you understand what I'm getting at.
Here it is:
Q) The large circle has a radius of 10cm. Within the large circle are 4 smaller circles as shown in the link below (the image on the far left). 'You may have to click on the image for the picture to be clear so you can see what I mean.' Find the radius of the largest circle which will fit in the middle.