Read the following conversation carefully!

Wisnu : How are you, Ranti?

Ranti : Wisnu! I'm good. How are you?

Wisnu : Fine, thanks. By the way, I have two free tickets.

Ranti : Tickets?

Wisnu : Yes. They are tickets for the painting exhibition which will be held next week at the YellowHall.

Ranti : : I know the event. I heard some information from a radio.

Wisnu : Will you come with me to the exhibition? We can observe and learn the paintings there.

Ranti : Thank you for thinking of me. But, I cannot go.

Wisnu : Oh, that's bad. You like painting, don't you?

Ranti : I do. I've just been preparing myself for the Mathematics Olympiad. I don't even have time to do my hobby.

Wisnu : You're so busy then.

Ranti : I'm sorry.

Wisnu : No problem. I'll invite someone else then.

Ranti : You should take someone, who likes painting too, to go with you.

Wisnu : You're right. I think I must go back to the classroom now.

Ranti : Okay. See you around.

Wisnu : See you around.

Why does Ranti refuse to go?