No. the first 3 is 300, the second 3 is 30, and the third 3 is 3
4 people email 3 more people each so 12 people are emailed, then these 12 people email 3 more people each, so 36 people are emailed.
The student is correct. Due to the meaning of perimeter which is all sides added up to make a number total, it is possible for a square and a rectangle to have the same perimeter if the numbers add up.
We have the frequencies for each of the grades. We can estimate the number of students graded by adding all those frequencies. Let's call N the total number of grades:

We have then a total number of grades of 39.
The corresponding relative frequency for a grade is the ratio of the frequency to the total number of "samples", 39 in this case.
Then, for grade A, the relative frequency (RF) will be:

This will be the fraction of the total grades that are A. Represented as a percentage will be 10.26%, rounded to two decimal places.
Now, to complete the table we do the same for the other frequencies:
For grade B:

For grade C:

For grade D:

For grade F:
The answer is 224.7 you got to turn 30% into decimal which is 0.30
then multiply 0.30 and 749 which equals 224.7