For number one they are simply multiplying the width by 2 and for the length, it would be 5 times 2 and you'll get 10 inches.
For number 2, you had to do 21 divided by 3 and get 7. Then find 10% of 21 which is 2.10. Then 2.10 divided by the three people is 0.7. So add 7 and .7 together and get $7.70
