Hannah and heather are sisters. hannah's age is four less than twice heather's age. the sum of their ages is 30. which system of equations can be used to determine hannah's age, x, and heather's age, y?

a.
x + 30 = y
x = 2 - 4y

b.
x + y = 30
x - 2y = 4

c.
x + y = 30
x = 2y - 4

d.
x + y = 4
y = 30 - 2x