book Maths Puzzle Numerical Ability

please make it clear how i open the brackets best thanx
17-(13x-(15-19x)-21x)=25-((11x-23)-(18x-7))

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book Other Question

hi
i want to ask that how can i find the sum of the equations like
1*+2*+......+n* where * = 2 How do I find the partial fraction decomposition of 7-8x/x2-x-2