How many solutions does cos^-1(0) have?

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

Find the value of the cosine for angle a

Antonia and carla have an equivalant percentage of green marbles in their bags of marbles. antonia has 4 green marbles and 16 total matbles. if carla has 10 green marbles , how many total marbles does carla have