Answer: You work backwards from the way it was set up. For example if you want to find the are of a triangle you would multiple the side lengths and then divide it by two, which gives you the area. To undo the equation you would work backwards. So lets say you only know one side, you would take the area of the triangle, multiply it by two( because we divided it the first time) and then divide the new number by one of the side lengths you know, this will leave you will the other side length. This is the principle you can go off of when trying to undo an algebra equation... Just work backwards.
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