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Answer:
c = 2A/w -b
Step-by-step explanation:
Multiply by the inverse of the coefficient of the parentheses.
[tex]A=\dfrac{w}{2}(b+c)\\\\\dfrac{2A}{w}=b+c\\\\\boxed{c=\dfrac{2A}{w}-b} \qquad\text{subtract $b$}[/tex]