1.Let B an nxn matrix such that B^4=0

Show that A=I-B is invertible and A^-1 = I+B+B^2+B^3?

2 Let A an nxn Matrix

a.If A^2=0 show that A is not Invertible

b. If A^2= A and A is not the identity, show that A is not Invertible.

plz help.. i couldnt seem to figure it out?