If the sum of the ages of a, b, and c is 60 years, and a is half the age of c, while b is the age of c minus the age of a, what ages are a, b, and c?
a) a = 15 years, b = 20 years, c = 25 years
b) a = 10 years, b = 30 years, c = 20 years
c) a = 12 years, b = 24 years, c = 24 years
d) a = 18 years, b = 22 years, c = 20 years