In parallelogram

Given, ∠TOF,∠TIS and ∠TIF

⟹In ∆TOF,

∠T + ∠O + ∠F = 180

25 + 110 + ∠SFT = 180

∠SFT = 180-135

∠SFT = 45

⟹In ∆TOS,

∠T + ∠O + ∠S = 180

35 + (180-110) + ∠OST = 180

35 + 70 + ∠OST = 180

∠OST = 180-105

∠OST = 75

∠STO = ∠T(in triangle SOT) = 35