A linear system AX=B

A= [1 2 3]

[4 5 6]

[7 c 9]

B= [1]

[2]

[b]

1) For what value of c are there no or infinitely many solutions?

2) For what value of b are there infinitely many solutions and what are they?

I know that ‘c’ is obviously 8 but I can’t figure out how to compute AX=B to obtain values of c and b. I even know that if c=8, there are infinitely many solutions. Please help me as I have been doing this for the past 2 days.