Answer:
gal --> L --> mL --> g --> lb --> tons
Explanations:
The following for calculating the density is expressed as;

Convert gallons to Litres
1 gallon = 3.785 liters
208,000 gallons = 787280Litres
Convert Litres to mL

Determine the mass

Convert grams to pounds

Convert pounds to tons

Based on the solution above, the correct map that outline the steps to find the weight of the water in a filled swimming pool in tons is gal --> L --> mL --> g --> lb --> tons