book Maths Puzzle Numerical Ability

I DON"T GET ALGEBRA AT ALL!!!! can somebody help me? this also for percentages.

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book Other Question

This problem has to do with permutations:Let n = 9
sigma = (2 3 7 5 6) and mu = (1 8 9 4)
1. Compute sigma of mu and mu of sigma
2. Compute sigma-squared and sigma-cubed. Find two consecutive positive integers such that the sum of
their squares is 85.

I got 6,7...is that correct/