First figure out how many city miles Carl will drive round trip by multiplying the one-way number of city miles by 2: 60 miles * 2 = <<60*2=120>>120 miles
Then figure out how many highway miles Carl will drive round trip by multiplying the one-way number of highway miles by 2: 200 miles * 2 = <<200*2=400>>400 miles
Now divide the round-trip number of city miles by the number of city miles per gallon Carl's car gets: 120 miles / 30 mpg = <<120/30=4>>4 gallons
Now divide the round-trip number of highway miles by the number of highway miles per gallon Carl's car gets: 400 miles / 40 mpg = <<400/40=10>>10 gallons
Now add the gallons for the highway miles and the city miles to find the total number of gallons Carl needs to buy: 10 gallons + 4 gallons = <<10+4=14>>14 gallons
Finally, multiply the number of gallons Carl needs to buy by the cost per gallon to find out how much he spends: 14 gallons * $3.00 = $<<14*3=42.00>>42.00
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