Given:
Number of tomatoes Sheldon picks = 
 kg
 kg
Rotten tomatoes = 1.5 kg
To find:
How many kilograms of tomatoes were not rotten?
Solution:
Number of tomatoes Sheldon picks = 
 kg
 kg
 = 
 kg
 kg
 = 
 kg
 kg
 = 
 kg
 kg
 = 
 kg
 kg
Rotten tomatoes = 1.5 kg
Remaining tomatoes which are not rotten is
Required tomatoes = Tomatoes Sheldon picks - Rotten tomatoes 
 = 

 = 
 kg
 kg
Therefore, the tomatoes which were not rotten is 2.9 kg.