C3 is pretty easy, I got an E and U in C1 and C2, did C3 and got an A (retook C1 and C2, got B and A respectively).
C4 isn't hard, but time is a real problem. I didn't get time to finish two full questions for C4 meaning I ended up with a C for it.
But like I said, C3 was a piece of cake, this is coming from someone that basically failed at AS Maths. AQA btw.