Correct answer: c = a - 5, d = b - 8
The positron emission decreases the atomic number by 1, each α-particle emission decreases the atomic number by 2 and mass number by 4, and β-particle emission does not affect the mass number but increases the atomic number by 1. After applying these changes step-by-step, the final relation is c = a - 5 and d = b - 8.