Which system of equations has infinite solutions?

Select one:

a.
7x + 4y = 6; 56x +3y = 18


b.
5x - y = 4; 1x +3y = 7


c.
11x - 7y = 4; 6x +89 = -3


d.
3x + y = 4; 6x +2y = 8