The correct option is B 25.21 km
Frist, we convert the given decimals into like fractions with denominator as 100.
23.4=23.40=2340100 [Traveled by bus]
1.81=181100 [Traveled by car]
Total distance he traveled = 23.4 + 1.81
=2340100+181100
=(2340+181)1000
=(2521)100
∴23.4 km+1.81 km=25.21 km