help with a further maths question

hey,

how would i solve 5(iii)? i’ve seemed to figure out i and ii but can’t get my head around iii.

many thanks.

One root of the quadratic equation x^2 + ax + b = 0, where an and b are real, is 16 - 30i.
(i) Write down the other root of the quadratic equation.
(ii) Find the values of a and b.

(iii) Use an algebraic method to solve the quartic equation y^4 + ay^2 + b = 0. (7 marks)