The fuel tank of an automobile has a capacity of 14.8 gallons. if the density of gasoline is 42.0 lb/ft^3, what us the mass of fuel in kilograms when the tank is full?

The capacity of the fuel tank = 14.8 gallons.
Note that
1 US gallon = 0.13368 ft³.
Therefore the capacity is
(14.8 gals)*(0.13368 ft³/gal) = 1.9785 ft³.

The density of gasoline is 42.0 lb/ft³, therefore the mass of gasoline is
(42 lb/ft³)*(1.9785 ft³) = 83.097 lb.

Because 1 lb = 0.4536 kg, the mass is
(83.097 lb)*(0.4536 kg/lb) = 37.693 kg

37.7 kg (nearest tenth)

The molecules contain like 54 of water