It says to estimate, so if I'm right, you would round each, add the new totals together, and then subtract that total from 20. 3.99 would be 4 dollars, 2.29 would round down to 2 dollars, and 6.75 rounds up to 7. 4+2+7=13. 20-13=7, so therefore, she would recieve about 7 dollars in change.
