Question 531192
This is pretty straightforward; the point of this problem is to see if you understand how to simplify equations.  The key to that is to combine all like terms:
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43 + a - 20 = -25
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If we subtract 43 and add 20 to both sides, on the left side of the equation we will just have "a"...and on the other side, we will have left what a =
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43 - 43 + a - 20 + 20 = -25 - 43 + 20
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a = -48
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cheers,
Lee