That depends on how "x" and "y" are related. For example, if you happen to know that there is a linear relationship, you can use the rule of three to calculate the missing value. But if you don't know how "x" and "y" are related, it can be ANYTHING.
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5x + 2 = x + 12 5x - x = 12 - 2 4x = 10 x = 10/4 x = 5/2 or 2.5
5-4x=12-2x isolate your x's on one side 5=12-2x+4x 5-12=-2x+4x simplify -7=2x divide by 2 x=-7/2, or x=-3.5
5 x 12/2.54...
-6/y=5/-2 5y=12 y=12/5
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2
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so 3x + 2 = x + 12 ie 2x = 10 x =5
5x + 2 = x + 12 5x - x = 12 - 2 4x = 10 x = 10/4 x = 5/2 or 2.5
x+2(x+3) = 12 x+2x+6 = 12 x+2x = 12-6 3x = 6 x = 2 and y = 5
5(-2)+(-3)(-4) =-(10)+12 =2
5-4x=12-2x isolate your x's on one side 5=12-2x+4x 5-12=-2x+4x simplify -7=2x divide by 2 x=-7/2, or x=-3.5
5 x 12/2.54...
12
5-x equals 7 = -2