Let a, b, c be the coefficients of the balanced reaction
a SF₄ + b O₂ ⇒ c OSF₄
The atom counts for each element among the reactants should be the same as with the products:
• S : a = c
• F : 4a = 4c
• O : 2b = c
If b = 1, it follows that a = c = 2. So the balanced reaction is
2 SF₄ + 1 O₂ ⇒ 2 OSF₄