Answer:
Required inequality is t ≤ 4.
Explanation:
There are 21 sheets of stickers.
Noor gave 1/3 of a sheet to each of the 45 students.
So, she gave 1 sheet to 3 students.
Therefore, the number of sheets she gave for 45 students =
.
Remaining sheets = 21 - 15 = 6
Now, the number of teachers = t
Number of sheets Noor gave to one teacher =

For t teachers, the total number of sheets given =
.
Clearly, this quantity should be less than or equal to the remaining sheets 6.
Hence, the required inequality is:

3t ≤ 12
t ≤ 4