Can two shelves of 0.72 meters long each store 50 30mm wide textbooks?

First, convert the units so you can compare more easily. 

0.72m = 72cm = 720mm

So 1 shelf is 720mm and 1 textbook is 30mm wide. 

To find the maximum number of books that can be stored on a shelf, you divide the length of the shelf by the width of the texbook. 

so 720/30= 24 textbooks

as there are two shelves, you times 24 by 2, which is 48. Hence the maximum number of textbooks that can be stored is 48. In conclusion, 50 textbooks cannot be stored on the shelves