6a+3(a-20)=399

Solution for 6a+3(a-20)=399 equation:

Simplifying
6a + 3(a + -20) = 399

Reorder the terms:
6a + 3(-20 + a) = 399
6a + (-20 * 3 + a * 3) = 399
6a + (-60 + 3a) = 399

Reorder the terms:
-60 + 6a + 3a = 399

Combine like terms: 6a + 3a = 9a
-60 + 9a = 399

Solving
-60 + 9a = 399

Solving for variable 'a'.

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

Add '60' to each side of the equation.
-60 + 60 + 9a = 399 + 60

Combine like terms: -60 + 60 = 0
0 + 9a = 399 + 60
9a = 399 + 60

Combine like terms: 399 + 60 = 459
9a = 459

Divide each side by '9'.
a = 51

Simplifying
a = 51