3(a+b)+6=21

Solution for 3(a+b)+6=21 equation:

Simplifying
3(a + b) + 6 = 21
(a * 3 + b * 3) + 6 = 21
(3a + 3b) + 6 = 21

Reorder the terms:
6 + 3a + 3b = 21

Solving
6 + 3a + 3b = 21

Solving for variable 'a'.

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

Add '-6' to each side of the equation.
6 + 3a + -6 + 3b = 21 + -6

Reorder the terms:
6 + -6 + 3a + 3b = 21 + -6

Combine like terms: 6 + -6 = 0
0 + 3a + 3b = 21 + -6
3a + 3b = 21 + -6

Combine like terms: 21 + -6 = 15
3a + 3b = 15

Add '-3b' to each side of the equation.
3a + 3b + -3b = 15 + -3b

Combine like terms: 3b + -3b = 0
3a + 0 = 15 + -3b
3a = 15 + -3b

Divide each side by '3'.
a = 5 + -1b

Simplifying
a = 5 + -1b