21-7(a+6)=42

Solution for 21-7(a+6)=42 equation:

Simplifying
21 + -7(a + 6) = 42

Reorder the terms:
21 + -7(6 + a) = 42
21 + (6 * -7 + a * -7) = 42
21 + (-42 + -7a) = 42

Combine like terms: 21 + -42 = -21
-21 + -7a = 42

Solving
-21 + -7a = 42

Solving for variable 'a'.

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

Add '21' to each side of the equation.
-21 + 21 + -7a = 42 + 21

Combine like terms: -21 + 21 = 0
0 + -7a = 42 + 21
-7a = 42 + 21

Combine like terms: 42 + 21 = 63
-7a = 63

Divide each side by '-7'.
a = -9

Simplifying
a = -9