B-I GOT IT

A young boy in a denim vest with a Union Jack on the back stands at a chalkboard in a classroom, turns to face the camera with a serious expression, and then turns back to the board where the equation "2+1=0K" is written. The scene cuts to another boy in a red jacket raising three fingers, then returns to the first boy, who turns again to reveal the back of his vest, before the camera focuses on the completed equation on the chalkboard.