First, see that 690 is approximately half of 1375.
So in total, we have two parts large bottles, and one part small bottle.
Now we can just add 1.89 + 1.89 + 1.38 and divide by 3 to get our answer.
If you do this calculation, we get exactly 1.72.
However, I would just add 1.9 + 1.9 + 1.4 = 5.2, and now divide by 3 to get 5.2/3 = 1.73
Because we rounded up (1.89 to 1.9 and 1.38 to 1.4) the answer is actually a bit less than 1.73, so the closest answer is 1.72, D.
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