Fiona earns 40 hours/week * $20/hour = $<<40*20=800>>800/week
So she earns $800/week * 4 weeks/month = $3200/month
John earns 30 hours/week * $20/hour = $<<30*20=600>>600/week
So he earns $600/week * 4 weeks/month = $<<600*4=2400>>2400/month
Jeremy earns 25 hours * $20/hour = $<<25*20=500>>500/week
So he earns $500/week * 4 weeks/month = $2000/month
Overall their boss has to spend $3200/month + $2400/month + $2000/month = $<<3200+2400+2000=7600>>7600/month
#### 7600