Book Maths Puzzle General Mental Ability

Can you please help me solve this problem: The page of a book is twice as high as it is wide, and there are margins 2cm wide at the top and sides of the page. The margin at the bot

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Book Other Question

Can you please explain to me how you find the answer to this problem: If two parallel sides of a square are increased by 6 cm and the other two parallel sides are each decreased by 1 cm, a rectangle is formed having twice the area of the square. How long was each side of the square? what are the steps for solving this equation?
-4x + 5y = -16
8x + y = - 1

do I need to eliminate the variables 1st?