Evaluate by complete u$-$substitution: ${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{3x}{3x+1}dx$ Show all $4$ Steps

Step $1$: What is U $$ Solve for x $$

Find $dx($in terms of $u)$

Step $2$ Substitute u$\text{'}$s into original equation

Step $3$: Evaluate using power, exp or $ln$ types

Step $4$ Put x$\text{'}$s back in$.$