for example, 2013 section b question 6, how do you find the center point of the circle with the radis 30?
If you look at the bottom right circle, it has a radius of 35
the distance between the centre point of that circle and the centre point of the circle at the top is then 75
you add them together to make 110
so you mark 110 from the bottom and draw a horizontal line and then mark 15 across from the centre point of the bottom right circle and where the two lines meet is your centre point for the 30 radius circle
please feel free to ask any more questions i'll be happy to answer or explain them