4. In some borane BxHy, the mass fraction of boron is 81.1%. The vapor density of this borane in air is 1.84 (air composition in mass fractions, %: N2 ─ 78.09; O2 ─ 20.95; Ar ─ 0.93; CO2 ─ 0.03). Determine the chemical formula of borane.

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