Final answer:
Sonu's age, given that Tony is z years old and Sonu is 5 years younger, can be expressed as z - 5.
Step-by-step explanation:
The question requires us to express Sonu's age in terms of Tony's age using basic algebra. Given that Tony is z years old, and Sonu is 5 years younger than Tony, we can represent Sonu's age as z - 5. This algebraic expression simply takes Tony's age (z) and subtracts 5 years to find Sonu's age. It is important to recognize the correct use of the word 'than' in this context, which is used to compare ages. The word 'then' is unrelated, as it indicates a sequence in time.