English to Arabic Bus/Financial Finance (general) finance مالية

Dear all,

I'm wondering what's the Arabic translation of (fat / lean utility bills) in the following context:

"Put her in charge of saving energy around the house
(turning off lights, unplugging chargers,
monitoring the thermostat), and offer her
a portion of the difference between your
fat and lean utility bills"

The writer advising the parents to assign tasks to their kids if they need to earn money.
Thanks.