m+3m-2+3(2m+1)=21

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

Simplifying
m + 3m + -2 + 3(2m + 1) = 21

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

Reorder the terms:
-2 + 3 + m + 3m + 6m = 21

Combine like terms: -2 + 3 = 1
1 + m + 3m + 6m = 21

Combine like terms: m + 3m = 4m
1 + 4m + 6m = 21

Combine like terms: 4m + 6m = 10m
1 + 10m = 21

Solving
1 + 10m = 21

Solving for variable 'm'.

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

Add '-1' to each side of the equation.
1 + -1 + 10m = 21 + -1

Combine like terms: 1 + -1 = 0
0 + 10m = 21 + -1
10m = 21 + -1

Combine like terms: 21 + -1 = 20
10m = 20

Divide each side by '10'.
m = 2

Simplifying
m = 2