Calculate and pay attention to the correct accuracy of the answer.

a) [[$ \text{53.12 km} + \text{12.3 km} \approx $]] km
b) [[$ \text{300.2 km} - \text{120.0311 km} \approx $]] km
c) [[$8000 \text{ km} + \text{0.75 km} \approx $]] km
d) [[$ \text{0.097 km} - \text{0.0006 km} \approx $]] km