Evaluating Expressions

Evaluate the following expressions.

1. $x-13$ when $x=17$

2. $23+x$ when $x=3$

3. $18.9+x$ when $x=2.31$

4. $3x^2-4x+5$ when $x=2$

5. $x^3+2x^2+3x-7$ when $x=7$

6. $\dfrac{2}{x}+\dfrac{5}{2x}$ when $x=3$

7. $4-3\dfrac{3}{x}$ when $x=4$

8. $\dfrac{9+x}{10x-4}$ when $x=5$

9. $\dfrac{14}{38}x$ when $x=\dfrac{19}{54}$

10. $3x+7y^2+2y$ when $x=12$ and $y=11$ 

11. $13x-21y+37z-8$  when $x=23$, $y=1.5$, and $z=0.2$

12. $y^2+2y-3x^2+x^3-4x$  when $x=5$ and $y=9$