Between 75 and 98.
Explanation:
Let's first have a look at the previous data available:
Friday, 27 dunk teachers out of 215 participants (12.5%)
Saturday: 54 dunk teachers out of 417 participants (12.9%)
Sunday: 39 dunk teachers out of 368 participants (10.6%)
So, based on the previous 3 days, she can expect between 10% and 13% will dunk a teacher.
If she has 750 contestants on Monday, the number of winners should then be in the range of 75 (10% of 750) and 98 (13% of 750).