The equation can be solved by performing the inverse of the operation that is done to the variable. Here, 12 is added to the variable. The inverse of that operation is addition of the "additive inverse", or "opposite" of 12:
12 + d = -4.8 . . . . . . given equation
12 -12 +d = -4.8 -12 . . . . . the same operation is done to both sides
d = -16.8
The value of d that makes the equation true is -16.8.
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The addition (subtraction) property of equality tells you that adding (subtracting) the same number from both sides of an equation will not change the value of the variable.
