First find how many ounces of carbon dioxide are released per shopping trip: 8 bags/trip * 4 oz/bag = <<8*4=32>>32 oz/trip
Then divide that amount by the number of ounces per pound to find the pounds of carbon per shopping trip: 32 oz/trip / 16 oz/pound = <<32/16=2>>2 pounds/trip
Then divide the amount of carbon used to make the tote bag by the amount of carbon saved per shopping trip to find the number of trips needed for the bag to be a better option: 600 pounds / 2 pounds/trip = <<600/2=300>>300 trips
#### 300