Answer:
4 x 10^12 kg Uranium
Step-by-step explanation:
As we know that 1 gallon = 3.785 L
Amount of Uranium in 1 L sea water = 3 x 10^-6 g
3.535 x 10^20 gallons = 3.535 x 10^20 x 3.785 L = 13.38 x 10^20 L
1 L of sea water contains = 3 x 10^-6 g Uranium
13.38 x 10^20 L of sea water contains = 13.38 x 10^20 x 3 x 10^-6 g Uranium
= 4 x 10^15 g = 4 x 10^12 kg Uranium