The points on a section of an exam is given by the function f(x), where x is the number of questions answered correctly in that section. If f(12)=18, then a test-taker receives 18 points for answering questions in the section correctly.

White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.