Evaluate the indefinite integrals using substitution. (Use $C$ for the constant of integration.)

1. $\displaystyle \int {\tan\!\left(3x\right)} \, dx =$
   Hint: First rewrite ${\tan\!\left(3x\right)}$ in terms of sine and cosine.
2. $\displaystyle \int {\sec\!\left(6x\right)} \, dx =$
   Hint: First multiply and divide by $\sec(6 x) + \tan(6 x)$.