The mathematical expression 9 & T means: 9 Intersection T
O 9 unlon T
9 is not an element of T
9 is an element of T

1. 9 union T is written as 9 ∪ T.

2.9 intersection T is written as 9 ∩ T.

3. 9 is an element of T is written as 9 ∈ T.

4. 9 is not an element of T is written as 9 ∉ T.

Therefore option 4 is correct.

32

Step-by-step explanation:

It is given that Jeff and his friend each text four classmates about an concert that is two people texts four classmates then 2×4=8 people are notified about the concert, then according to question, each 8 of them texts 4 more students from a different school about the concert,  so the total number of people from the other school which are being notified about the concert will be 8×4=32.