Answered the first part of the question:

What is the probability that we could randomly select a student whose grade is at least 70? What is the likelihood that a student enrolled in maths has a mark at least 70?

Probability that a randomly selected studentís mark is at least 70: 73.54%

353 students with a grade of at least 70 / 480 students total

Likelihood that a student enrolled in maths has a grade at least 70: 61.21%

71 students with a grade of at least 70 who are enrolled in maths / 116 students enrolled in math

The part of the question I am unsure of: Is the grade statistically independent of whether they are enrolled in maths? Use a Contingency Table.

I think that they are not statistically independent because the grades from math come from the grades overall but I don't know if that is correct and use a contingency table to prove it or otherwise.