What is the internal energy of hydrogen filling a 20 cubic meter balloon at a pressure of 10 kPa?

V = 20 m ^ 3
p = 10 kPa = 10 * 10 ^ 3 Pa
U -?
U = 3/2 * m / M * R * T, where m is the mass of hydrogen, M is the molar mass of hydrogen, R is the universal gas constant, T is the temperature of hydrogen
since the temperature is unknown to us, we use the Cliperon-Mendeleev equation
p * V = m / M * R * T
U = 3/2 * p * V
U = 3/2 * 10 * 10 ^ 3 * 20 = 3 * 10 ^ 5 J = 300 kJ