.3(21-3a)=6-a

Solution for .3(21-3a)=6-a equation:

Simplifying
0.3(21 + -3a) = 6 + -1a
(21 * 0.3 + -3a * 0.3) = 6 + -1a
(6.3 + -0.9a) = 6 + -1a

Solving
6.3 + -0.9a = 6 + -1a

Solving for variable 'a'.

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

Add 'a' to each side of the equation.
6.3 + -0.9a + a = 6 + -1a + a

Combine like terms: -0.9a + a = 0.1a
6.3 + 0.1a = 6 + -1a + a

Combine like terms: -1a + a = 0
6.3 + 0.1a = 6 + 0
6.3 + 0.1a = 6

Add '-6.3' to each side of the equation.
6.3 + -6.3 + 0.1a = 6 + -6.3

Combine like terms: 6.3 + -6.3 = 0.0
0.0 + 0.1a = 6 + -6.3
0.1a = 6 + -6.3

Combine like terms: 6 + -6.3 = -0.3
0.1a = -0.3

Divide each side by '0.1'.
a = -3

Simplifying
a = -3