1) The applicable formula is
I = Prt
I = $30,000×0.095×(120/365)
I ≈ $936.99
2) The same formula applies.
I = $30,000×0.095×(85/365)
I ≈ $663.70
3a) The interest due on day 30 is
I = $30,000×0.095×(30/365) ≈ $234.25
so the new balance is $30,000 - $10,000 + $234.25 = 20,234.25
3b) The amount due on day 85 is
A = P(1 + rt) = $20,234.25·(1 + 0.095·((85-30)/365))
A = $20,523.90