book Maths Puzzle Numerical Ability

could you explain the steps on how to do it? for example A=20 C=29

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book Other Question

the number which best completes the sequence 39 9 4 5 25 20 21 441? Factor completely: 36(x^4)y + 12(x^3)y^2 - 15(x^2)(y^3)

Thank you
D. Scarfone