The problem says that the container can be loaded with a maximun weight of 26000 kg.
Also, other shipments weighing 12900 kg have already been loaded into the container, which means you need to subtract this to the maximum weight in order to know what is the actual capacity of the container, then:
![26000\operatorname{kg}-12900\operatorname{kg}=13100\operatorname{kg}]()
Each crate weighs 150 kg, and you need to know what is the greatest number of crates that can be loaded, thus, you have to divide the capacity available into the weight of the crates, thus:
![\frac{13100\operatorname{kg}}{150\text{ kg/crate}}=87.33\text{ crates}]()
Then, the greatest number of 150-kg crates that can be loaded into the shipping container is 87.