I need help with number 5

Answer:
C) 27.8 m
Step-by-step explanation:
The law of cosines applies.
c^2 = a^2 + b^2 - 2ab·cos(C)
c^2 = 18^2 + 17^2 -2·18·17·cos(105°) . . . . fill in the given dimensions
c^2 ≈ 771.3973
c ≈ √771.3973 ≈ 27.8 . . . . meters