To find out how much each of them earns for 20 hours we need to find how much they earn per hour. To do that we need to find the constant of proportionality for each of them:
In Savannah's case we have:
In Greg's case we have:
In Kevin's case we have:
Now that we have each of the constant of proportionality we multiply them by 20 to find out how much each of them earn for 20 hours.
Therefore Savannah earns $190, Greg earns $180 and Kevin earns $165 for 20 horus of work.