Suppose you sequentially add 10 drops of water to a graduated cylinder and read the volume add 10 more drops read and so on. how many total drops will have been added after you do this four times

It depends on what is being referred to by "this."

The description of the activity is that 10 drops are added twice and two readings are taken. If you do *that* 4 times, then a total of 20*4 = 80 drops will have been added.

If the activity referred to by "this" is the pair of acts {add 10 drops, read the volume}, then four repetitions will have added 10*4 = 40 drops.

Probably the expected interpretation is that "this" is {add 10 drops, read}, so 40 drops is likely the expected answer.