book Maths Puzzle Numerical Ability

I need help on this problem. Thankx
What is Sn for the arithmetic series with d = -4, an = 27, and n = 9?

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book Other Question

The area of a triangular plate is 16cm^2. If the base is 1cm longer than the height, what are the lengths of its base and height?
I am really unsure how to tackle this question. 14xsquared + 35x + 21 / 12xsquared + 30x +18

cant figure out how to do it