This question depends on how would you like to do. However, I solve this question with the premise, the breads are not cut into halves or anyway.
The concept used is ratio. Quite simple :
a) 16/20= 4(4/5) (simplify)
there for 4 containers are needed.
b) Since we can express the total number of breads in form of ratio, thus it will be:
4:5, which means that 4 french breads and 5 garlic breads in each container.