For the following question (which I pulled of the internet)
A five member committee is to be selected from among four Math teachers and five English teachers. In how many different ways can the committee be formed under the following circumstance?
A) Anyone is eligible to serve on the committee.
B) The committee must consist of $3$ Math teachers and $2$ English teachers.
C) The committee must contain at least three Math teachers.
D) The committee must contain at least three English teachers.
(Answer $126$, $40$, $45$, $81$)
How would I go about solving when the requirement is at least $3$ Math Teacher Any suggestions ? . I know that when it was $3$ Math and $2$ English teachers I simply took r=3 for math and r=2 for English in the Combination Formula.