(a) The minimum grade that Lamond can receive on the sixth exam to pass the course is \(\boxed{50}\).
(b) To get a C, Lamond needs an average of 70, which means a total score of:
\[
70 \times 6 = 420
\]
Since his current total is 310, the score needed on the sixth exam is:
\[
420 - 310 = 110
\]
Since 110 is not a possible score on a single exam, it is not possible for Lamond to get a C.
(b) It is not possible for Lamond to get a C.