For a) use those existing equations you had to prove a manipulate them to get your answer for c), i.e. sub b=M into both (i) and (ii) then equate (i) and (ii) and simplify and you should get your answer for one of them, and similarly do it for the other one
For your second question I'm guessing to use the product of roots and use the existing answers you have to get your answer for part (c)