Answer is 342.6 torr.
Step-by-step explanation:
Let's assume that the gas in the balloon is an ideal gas.
Then we can use combined gas law,
PV/T = k (constant)
Where, P is the pressure of the gas, V is volume of the gas and T is the temperature of the gas in Kelvin.
For two situations, we can use that as,
P₁V₁/T₁= P₂V₂/T₂
P₁ = ?
V₁ = 2.58 L
T₁ = 368 K
P₂ = 777 torr
V₂ = 1.53 L
T₂ = 495 K
From substitution,
P₁ x 2.58 L / 368 K = 777 torr x 1.53 L / 495 K
P₁ = 342.6 torr
Hence, the answer is 342.6 torr.