Find m PLEASE HELP 10 POINTS!!

Answer:
(D). 17 in.
Step-by-step explanation:
c² = a² + b² - 2abcosC
cosC = [tex]\frac{a^2 + b^2 -c^2}{2ab}[/tex]
m∠C = [tex]cos^{-1}[/tex] ( [tex]\frac{a^2 + b^2 -c^2}{2ab}[/tex] )
m∠C = [tex]cos^{-1}[/tex] ( [tex]\frac{28^2 +18^2 -12^2 }{2(28)(18)}[/tex] )
m∠C = [tex]cos^{-1}[/tex] ( [tex]\frac{964}{1008}[/tex] ) ≈ 17 in.