People's Education Publishing House, the first day, the second volume, the answer to the seventh question on page 77.
Solution: ∫B is 45°C west-south of point A, and east-south of point A 15.
∴∠BAC=45+ 15=60
∴A is at 45 degrees north latitude at most.
At point B, C is 80 degrees east of north.
∴∠ABC=80-45=35
∴∠ACB= 180-35-60=85