Math problems are only for smart people

Using your reasoning and calculation skills, find the answer after the question mark. Stay calm and conquer this interesting question.

Can you solve this tricky puzzle?

Please observe carefully to give the correct answer.

Quickly register yourself in the top smartest people by leaving your answer in the comment box below.

Trung Temple

Source: https://vtc.vn/bai-toan-chi-danh-cho-nguoi-thong-minh-ar835968.html