That will depend on temperature change between the two places. I can show you the answer if we assume that the temperature doesn't change, but that's so unlikely between 2 places where the pressure changes by 50% that it's going to be a very unhelpful answer.
We also have to assume that the air in the balloon acts like an "ideal gas".
For an ideal gas at constant temperature, the product of
(pressure) x (volume)
is a constant number.
The balloon starts with pressure = 2.7 bar and volume = 8 L. The product is 21.6 bar-liter. If the temperature doesn't change, then that number won't change either.
The balloon is moved to a place where pressure = 1.3 bar. Since the temperature doesn't change, we know that (press) x (vol) is still 21.6 bar-liter. So we can write . . .
