21=3n+3(2n+1)

Solution for 21=3n+3(2n+1) equation:

Simplifying
21 = 3n + 3(2n + 1)

Reorder the terms:
21 = 3n + 3(1 + 2n)
21 = 3n + (1 * 3 + 2n * 3)
21 = 3n + (3 + 6n)

Reorder the terms:
21 = 3 + 3n + 6n

Combine like terms: 3n + 6n = 9n
21 = 3 + 9n

Solving
21 = 3 + 9n

Solving for variable 'n'.

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

Add '-9n' to each side of the equation.
21 + -9n = 3 + 9n + -9n

Combine like terms: 9n + -9n = 0
21 + -9n = 3 + 0
21 + -9n = 3

Add '-21' to each side of the equation.
21 + -21 + -9n = 3 + -21

Combine like terms: 21 + -21 = 0
0 + -9n = 3 + -21
-9n = 3 + -21

Combine like terms: 3 + -21 = -18
-9n = -18

Divide each side by '-9'.
n = 2

Simplifying
n = 2