Problem:
Joey is having a party. He has 10 friends, but his mom told him he could only invite 6 of them. How many choices are there if
a. there are no restrictions
b. there are 2 brothers who will only attend if they can attend together
c. there are 2 girls who each will not attend if the other one does
Provide complete and step by step solution for the question and show calculations and use formulas.