book Maths Puzzle Numerical Ability

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?

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book Other Question

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

x2 - 6x - 3 = 0 Is it correct to say the reciprocal of .25 is 1/.25 or do you convert the decimal to a fraction 25/100 and then flip?