Where does the name china come from?

The name 'China' comes from the Sanskrit Cina (derived from the name of the Chinese Qin Dynasty, pronounced 'Chin') which was translated as 'Cin' by the Persians and seems to have become popularized through trade along the Silk Road from China to the rest of the world.

7.03-1.70=5.33 and 6.80+5.09=11.89 and 5.5-3.01=2.49

a and b because with the other three, they simplify to something else.