I want to know what

3 + 4x = - 13 - 4x

Solution: x = - 2

to solve for x:

3+4x=-13-4x

move variable to the left side and change its sign.

move constant to the right side and change its sign.

collect like terms

calculate the difference

divide both sids by 8

solution: x=-2

3 + 4x + 13 = - 14x

4x + 16 = - 14x

16 = - 14x - 4x

16 = - 18x

- 16/18 x

-8 / 9 = x

x = - 9/8