The sum of two positive integers, a and b, is at least 30. The difference of the two integers is at least 10. If b is the greater integer, which system of inequalities couri represent the values of a and b?
a + b ≥ 30, b ≥ a + 10
a + b ≥ 30, b ≤ a - 10
a + b ≤ 30, b ≥ a + 10
a + b ≤ 30, b ≤ a - 10