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Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

Adam drew two same size rectangles and divided them into the same number of equal parts. he shaded 1/3 of one rectangle and 1/4 of the other rectangle. what is the least number of parts into which both rectangles could be divided into?

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4