MATH -- solve factorial..急問!

Slove the following equations.

1.
nC3=5nC1

2.
nC1+nC2=3n

3.
2nC1+nC0=9

4.
nC(n-2)=28


Simplify the following expressions.

5.
(n+2)C3-nC3

6.
(n-1)C(n-2)*(n-2)C(n-4)