3a-21a+6a-42=

Solution for 3a-21a+6a-42= equation:

Simplifying
3a + -21a + 6a + -42 = 0

Reorder the terms:
-42 + 3a + -21a + 6a = 0

Combine like terms: 3a + -21a = -18a
-42 + -18a + 6a = 0

Combine like terms: -18a + 6a = -12a
-42 + -12a = 0

Solving
-42 + -12a = 0

Solving for variable 'a'.

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

Add '42' to each side of the equation.
-42 + 42 + -12a = 0 + 42

Combine like terms: -42 + 42 = 0
0 + -12a = 0 + 42
-12a = 0 + 42

Combine like terms: 0 + 42 = 42
-12a = 42

Divide each side by '-12'.
a = -3.5

Simplifying
a = -3.5