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Given the equation :

So, to find d , divide both sides by ( -6 )
So,

Note: when we divide two negative numbers, the result will be a positive number
Answer: Estimates vary, but each person uses about 80-100 gallons of water per day
It should be 5/13 because the opposite angle from D is 12, which you would use if you are looking for sine. But, since you are looking for cosine, it is adjacent over hypotenuse. Therefore leaving you with 5/13, since your hypotenuse is always your longest side and the adjacent is the other side from the one opposite of the angle.