I am a little confused.

If they created 2 questions per day, 1410 is correct answer, right? Correct me if I’m wrong.

They add 2 questions every 3 days.

exactly, so 1410 is wrong?

No it’s correct! Currently the website has 770 questions and 2 qs are added every 3 days . So that’s nothing but 770+2d/3. Now the student has already completed 300 questions and plans on completing one q per day after that so the eqn is 300+d. Since both the eqns talk about the total number of problems they need to be equal. so 770+2d/3=300+d

When you simplify you get 470=d/3 so d=1410 days

Thank you!