Can you figure out easy-looking math sum in 30 seconds by remembering the special rule?

The answer to this mathematical brain teaser is NOT 40 - can YOU solve it in 30 seconds by remembering the special rule?

What to know about the Strait of Hormuz as Iran plans military drill while tensions are high with US

Iran plans a military drill in the Strait of Hormuz, a crucial global shipping lane. The drill, scheduled for Sunday and Monday, could involve live fire in the area where a fifth of the world's traded ...