Law of Cosine/Sine problem.

Answer:
[tex]\displaystyle 12,766277792...[/tex]
Explanation:
Solving for Angles
[tex]\displaystyle \frac{sin\angle{C}}{c} = \frac{sin\angle{B}}{b} = \frac{sin\angle{A}}{a}[/tex]
Do not forget to use [tex]\displaystyle arcsin[/tex] or [tex]\displaystyle sin^{-1}[/tex]towards the end, or the result will be thrown off.
Solving for Edges
[tex]\displaystyle \frac{c}{sin\angle{C}} = \frac{b}{sin\angle{B}} = \frac{a}{sin\angle{A}}[/tex]
Well, let us get to work:
[tex]\displaystyle \frac{18}{sin\:115} = \frac{c}{sin\:40} \hookrightarrow \frac{18sin\:40}{sin\:115} = c \\ \\ \boxed{12,766277792... = c}[/tex]
I am joyous to assist you at any time.