Please solve it quickly, I am now in the exam

Suppose we have 13 students, 8 of them are CS and 5 are ENCS, 7 of them are female and 6 are male. Suppose we want to form a group of 7 students, what is the probability of having at most three females in the group? Explain your answer in every step and make sure to calculate the final results and show how the calculation was done in every step. and you should use the counting laws and theories learned in chapter 9