(7a-21)+(a+4)=15

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Solution for (7a-21)+(a+4)=15 equation:


Simplifying
(7a + -21) + (a + 4) = 15

Reorder the terms:
(-21 + 7a) + (a + 4) = 15

Remove parenthesis around (-21 + 7a)
-21 + 7a + (a + 4) = 15

Reorder the terms:
-21 + 7a + (4 + a) = 15

Remove parenthesis around (4 + a)
-21 + 7a + 4 + a = 15

Reorder the terms:
-21 + 4 + 7a + a = 15

Combine like terms: -21 + 4 = -17
-17 + 7a + a = 15

Combine like terms: 7a + a = 8a
-17 + 8a = 15

Solving
-17 + 8a = 15

Solving for variable 'a'.

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

Add '17' to each side of the equation.
-17 + 17 + 8a = 15 + 17

Combine like terms: -17 + 17 = 0
0 + 8a = 15 + 17
8a = 15 + 17

Combine like terms: 15 + 17 = 32
8a = 32

Divide each side by '8'.
a = 4

Simplifying
a = 4

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