Vocal Was Sogolon + Enduring Harmony

Ok here's a question: Do Vocal Was Sogolon and Enduring Harmony stack and how do they stack?

Assuming we have 50% longer duration VWS, do they stack:
X sec + (0.5 * X) + (0.5 * X) = 100 % extended duration

or

X sec * 1.5 * 1.5? = 125% extended duration


Also do buffed durations get rounded to nearest second or not. For instance if you have 50% duration boost on 5 sec shout like Incoming!, does it last:

a) 7 sec
b) 7.5 sec
c) 8 sec

?

Thx.

good question, be nice if it doubled it, but i would assume it works like 125%