In the Avengers League, there are $25$ superheroes. Six of the superheroes from the galaxy guard left. How many heroes are left?~(adapted from $$2007$$ Math kangaroo Problems, Level $$1-2$$, Question \#$$6$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction->Simple Addition and Subtraction
There are $25$ superheroes in total. After subtracting $6$, there are $25-6=19$ left. 