The process used in the picture is cross multiplying. Make an x through the numbers and multiply them by each other. That's why 21 was multiplied by 14 and 49 was multiplied by n. The value of n is unknown, so it simplifies to 49n, and 14*21=21.4. So basically to recap, make an x, multiply the terms that are diagonal from each other, write both of the answers next to each other, and put an = sign in between them. If you don't understand I can try to explain differently ☺
