When all three sides and an angle in a triangle are involved, you must use the cosine rule.
a^2 = b^2 + c^2 - 2bc cos A, where A is the angle opposite side a.
When you substitute the values in, you get
a^2 = 324 + 289 - 612 cos(118)
a^2 = 497.25
So, a = 22.30 m
