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This sounds kind of like a homework problem. I assume the dimensions are 7 cm by 3 cm to start with. The original area is (7 cm)(3 cm) = 21 cm². The final area is 21 cm² + 85.25 cm² = 106.25 cm². Increase each dimension by the same amount:

(7 + x)(3 + x) = 106.25 ---> 21 + 10x + x² = 106.25 ---> x² + 10x - 85.25 = 0 Solve this quadratic (I used the quadratic formula) x = 5.5 or -15.5. So we cannot have a negative dimension, so add 5.5 cm to each dimension. Check it out with (12.5 cm)(8.5 cm) = 106.25 cm²

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Q: What are the new dimensions of a 7 by 3 rectangle when its dimensions are increased by equal amounts giving an extra 85.25 square cm to its area showing work?
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