After taking 15 cups of flour out of a bag, 3 cups of flour remained. how many cups of flour were in the bag to start? a. 3 - 15 = f b. f 15 = 3 c. 15 + f = 3 d. 3 f = 15 e. 3 + f = 15 f. f - 15 = 3

The answer is F.
If we call the bag of flour f, the bag needs to remove 15 cups, which is f-15. Then only 3 cups remained. So, on the other side of the equals sign, we get a 3.

So the answer is f-15 = 3. 
Hope this helps!