Answer:
67.88°
Step-by-step explanation:
If three sides of a triangle are known and you want to determine one angle, this can be done using cosine rule.
Given sides x, y, and z and the angle Y is opposite to side y, the cosine formula is given as:
y² = x² + z² - 2xzcosY
For this problem, x = 400 miles, y = 599 miles, z = 320 miles.
Using the cosine formula:

Degree to adjust its route at point Y = 180° - 112.12° = 67.88°
It needs to adjust by 67.88° at point Y