book Maths Puzzle Numerical Ability

please help me with this problem..
solve using the quadratic formula.
9d^2-81=0

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book Other Question

how do u find the intercepts of the line ? Simplify and evaluate:
(x2y-4z0/3x6y-3)4

= x^8 y616 z/12x^24 y 12

= y^4 z 12x^16

Could you tell me if I did this right and if not could you help me please? Thanks