Why is human blood type an example of multiple alleles? codominance?

It is because when alleles show a co-dominant relationship , neither allele is dominant and both are expressed in the phenotype of the heterozygote. The human ABO blood groups provide a good example of codominace. The ABO system is due to a gene that codes for molecules on the surface of red blood cells

Centimeter = 1/100 of a Meter
Kilometer = 1000 Meters

86,000/100 = 860 Meters
860/1000 = 0.86 Kilometers