Answer:
Expression y = 20 - 3x represents the total amount of change she should receive.
Explanation:
Given : Alexis bought x boxes of cereal for $3 each that is including tax
This can be written mathematically as 3x.
Let the total amount of change she should receive be denoted by y
The total amount she paid is $20
The whole scenario can be written as a single expression as,
3x + y = 20
As 20 includes the cost of x boxes and the change she received (y)
y = 20 - 3x
Thus, expression y = 20 - 3x represents the total amount of change she should receive.