Doris earns $20 per hour by babysitting. She needs to earn at least $1200 for her monthly expenses. She can babysit for 3 hours every weekday and 5 hours on a Saturday.  How many weeks does it take for Doris to earn enough to cover her monthly expenses?
Doris babysits for a total of 5 weekdays x 3 hours/weekday = 15 hours
She babysits for a total of 15 + 5 = 20 hours in a week.
She earns 24 x $20 = $480 in a week.
So, it will take $1440/$480 = 3 weeks to earn Doris needed amount.