When the 2 graphs are the same. It'll be infinitely many solutions.
System Equations are to find the intercepts of graphs so just think that when 2 graphs are same, that means they both intercept each others infinitely.
My prediction is that she didn't pick green any of the times when im assuming that she only picked from the bag 50 times. plus if you add 13 blue 18 green 19 pink you get 50 which is the number she put the marbles back