Extremely easy math problem for elementary school students but adults give up

Based on the available data, find the missing number in the third star below. To find the answer in a short time, the person doing it must have logical thinking and the ability to calculate quickly. It is known that this is a type of math that is not easy to conquer, often appearing in IQ tests.

Find the missing number in a short time, you are definitely the owner of an IQ that makes many people jealous. Comment the answer you found and see how many people have the same answer as you.

Hieu Lam

Source: https://vtcnews.vn/bai-toan-cuc-de-cua-hoc-sinh-tieu-hoc-nhung-nguoi-lon-deu-chao-thua-ar906629.html