In which ones do i use elimination or substitution?

For a read-a-thon, jay and odhràn each started reading a book at the same time and continued reading for several hours. jay's book had 278 pages, and he read 55 pages per hour. odhràn's book had 238 pages, and he read 45 pages per hour. after how many hours did they have the same number of pages left, and how many pages were left?

Ametal rod is 2/5 meters long. it will be cut into pieces that are each 1/30 meters long. how many pieces will be made from the rod?

How many quarts of a 50% solution of acid must be added to 20 quarts of a 20% solution of acid in order to get a 40% solution of acid?