Can someone me out with #4? show me how you got the answer.

Q1) jin loves carrot yesterday she ate ½ of here carrots and today she ate 2/3 of the remaining carrots. she then discover that she has 12 carrots left. yesterday she must has started with carrots? a)36 b)48 c)60 d)72

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

What term makes it inconsistent y=2x - 4