21=2a-4

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Solution for 21=2a-4 equation:


Simplifying
21 = 2a + -4

Reorder the terms:
21 = -4 + 2a

Solving
21 = -4 + 2a

Solving for variable 'a'.

Move all terms containing a to the left, all other terms to the right.

Add '-2a' to each side of the equation.
21 + -2a = -4 + 2a + -2a

Combine like terms: 2a + -2a = 0
21 + -2a = -4 + 0
21 + -2a = -4

Add '-21' to each side of the equation.
21 + -21 + -2a = -4 + -21

Combine like terms: 21 + -21 = 0
0 + -2a = -4 + -21
-2a = -4 + -21

Combine like terms: -4 + -21 = -25
-2a = -25

Divide each side by '-2'.
a = 12.5

Simplifying
a = 12.5

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