b) Substitute , substitute w = sin(x), re-arrange into a quadratic equation, solve for w and hence get two simple trig equations to solve.
c) See b).
d) Substitute and , re-arrange to get and solve for x.
I strongly advise that you find a textbook that explains this topic and has examples to follow. We cannot tutor you in material you have not been taught. And I don't see that there's any point at all in trying to do questions based on material you have not been taught. Clearly you are expected to review this material prior to attempting the questions.