Final answer:
The problem involves algebraic expressions for the ages of Sally, Mike, and Joe, based on Sally being y years old. Mike is 20 - y years old, while Joe is 3y - 4 years old.
Step-by-step explanation:
The student's question involves creating expressions to describe the ages of three individuals, Sally, Mike, and Joe, based on Sally's age being represented by the variable y. Sally's age is y years old. Mike's age is the difference between 20 and Sally's age, which can be represented by the expression 20 - y. Joe's age is described as being four years less than triple Sally's age, so his age can be represented by the expression 3y - 4. This question falls into the realm of basic algebra, which is typically covered in middle school mathematics.