exam Maths Puzzle Numerical Ability

How many gallons of a 12% solution must be mixed with a 32% solution to obtain 180 gals. of 22% solution?

Im not sure how to get this

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exam Other Question

three times a number less than forty-five is equal to twice the same number. prove that the sum of the angles of any quadrilateral is 360 degrees.

does it have to do with the expression: (n-2)180
where n is the number of sides?