The horizontal angle between two direction AB and AC, i.e. angleBAC, is measured with an uncertainty of ±7.3′′. The bearing of line AB, i.e. Brg(AB), was also measured with an uncertainty of ±2.5′′. A surveyor calculates the bearing of line AC as follows:

Brg(AC) = Brg(AB) - angleBAC

What is the standard deviation of the calculated bearing of line AC? Provide your answer in sexagesimal