My usual do not do the whole question rule is in effect.
I assume points A and B only just touch the circle.
Go back to triangles for this one and you will need radians on a calculator.
You have a triangle 10 cm (aka the radius) above point A.
You have one side 7cm long and the other is again the radius (10cm)
Need the angle now.
simple trigonometry gives us this one.
add pi/2 (90 degrees if you are still working in degrees for some reason).
Arc length is explained here:
http://www.themathpage.com/aTrig/arc-length.htm
pi x diameter = circumference (not so important now but you will need it in a minute)
the point on the circle is 2 cm above B in the vertical sense or 8cm below the horizontal radius.
repeat first part to get angle. This time however you have 1.5 times pi (or 270 degrees if again you are still in degrees)
Now you have the angles/lengths and whatever and knowing the diameter of the circle (you do not actually need it but it may help alleviate some of the confusion if you do it that way) you can work out distance travelled fairly easily.