6 exams for science, I don't believe you did 6 sit down exams for science.
3 sit down exams for maths.
Science was three separate subjects - biology, physics, chemistry. I did biology - a practical and a written exam. I suppose it was the same for the others. So someone who did all three would have six exams.
Maths as I recall was three papers - algebra, arithmetic and geometry.
French - oral, dictation, I think, and another written paper.
History - one paper for British history, one for European.
English language I think might have been two - an essay and a grammar/comprehension paper.
Can't remember Eng. Lit., Geography and Art.
And yes, the papers were two or three hours.