If Mary earns 7$ an hour, we need to multiplicate 7$ by the number of hours worked for the entire week so we can get the salary per week. And when we want to know how many hours she had worked, we have to "transform" the equation :
Salary per week = salary per hours x worked hours
Here, we know to informations : salary per hours and salary per week.
Worked hours = salary per week / salary per day
Worked hours = 143.50 / 7
Worked hours = 20.5
The greatest number of hours thats he works is 20h30.
