Answer: There is 225 millimeters of slushy originally in the cup.
Step-by-step explanation:
Since we have given that
Rate at which she drink the slushy = 4.5 millimeters
Time taken to drink the slushy by Mariana = 17 seconds
Total quantity she drank is given by

Still there is left some slushy,
Quantity of slushy left =148.5 millimeters
Total quantity of slushy originally in the cup was given by

Hence, there is 225 millimeters of slushy originally in the cup.