If the original was black and white, and if you had no way of knowing they were different colors, that still doesn't explain why you would think you were supposed to add all the balloons together. The unit was about subtraction. The question was "How many more
are there?" Do you see that word "more" in there? It means something. More than what? It certainly doesn't mean "add all the balloons together." The only way the problem makes any sense is if the balloons are different. If the teacher failed to explain to the children that the balloons were different colors, any adult reading the problem should have guessed as much. The teacher may have erred in handing out black and white copies of a test that was originally in color without explaining it to the children, but any grownup who understands that words mean things should have instantly understood. It looks from the markings on the paper that the teacher went on to explain it to the child, and it took less effort than trying to explain it to you.