Distance traveled = 400 km
Volume of gas = 47.2 L
Note that
1 km = 0.62137 mi, or 1 mi = 1.609 km
1 L = 0.264 gal (US)
Therefore
400 km = (400 km)*(0.62137 mi/km) = 248.548 mi
47.2 L = (47.2 L)*(0.264 gal/L) = 12.4608 gal
The gas mileage is
(248.548 mi)/(12.4608 gal) = 19.95 mi/gal
Answer: 20.0 miles per gallon (nearest tenth)
