book Maths Puzzle Numerical Ability

Addition seems simple enough to me, but the minus/negative numbers confuse me on factoring.

x2 - 6x - 3 = 0

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book Other Question

Write this phrase in algebraic terms: Seven times the sum of a number and a second
number is the product of five and the second number.
A) 7x + y = 5y B) 7(x + y) = 5 + y C) 7x + y = 5 + y D) 7(x + y) = 5y
A plane flies 420 miles with the wind and 350 miles against the wind in the same length of time. If the speed of the wind is 23 mph, what is the speed of the plane in still air?