On weekdays it earns $600/weekday * 5 weekdays = $<<600*5=3000>>3000
During the weekend it earns twice as much each day so it makes ($600 * 2)/weekend day * 2 weekend days = $<<(600*2)*2=2400>>2400
Every week it earns $3000 + $2400 = $<<3000+2400=5400>>5400
By the end of the month, it earns $5400/week * 4 weeks = $21600
#### 21600