First find how much Mary pays weekly for the trash bins: $10/trash bin * 2 trash bins = $<<10*2=20>>20
Then add this to the cost of the recycling bin: $20 + $5 = $<<20+5=25>>25
Then multiply the week cost by the number of weeks per month to find the monthly cost: $25/week * 4 weeks/month = $<<25*4=100>>100/month
Now calculate Mary's senior discount: 18% * $100 = $<<18*.01*100=18>>18
Now subtract the discount and add the fine to find the total monthly cost: $100 - $18 + $20 = $<<100-18+20=102>>102
#### 102