4/9 plus 2/5 would be 38/45, and the work is you must change the denominators to the same thing, so you do 4/9 * 5/5, like, multiply the top and the bottom by 5, to get you 20/45, and then for 2/5, multiply the top and the bottom by 9, to get 18/45, add them to get 38/45, and it can't be simplified.