Concept:In short replies, "So + auxiliary + subject" is used to agree with a positive statement.Explanation:Tayo makes a positive statement: "I think I can now solve the problem."Essien wants to say that he also thinks he can solve it.The verb "think" is in the present tense, so the auxiliary "do" is used to replace it.Therefore, the correct agreeing reply is "So do I."This means "I also think so."Answer:So do I.