How many genotypes are possible?

Coloration in butterflies is determined by four alleles at a single locus. R, B, b, and y
which encode red, black, blue or yellow respectively. It was found that red is dominant
over all other alleles, black is dominant over blue and yellow, blue is dominant over
yellow and yellow is recessive to all of the others.
a. How many genotypes are possible.
b. Give the possible genotypes and phenotypes.
c. If you crossed a red butterfly with a blue butterfly and got a 1:2:1 ratio of blue to red
to yellow offspring, what would be the genotype of the parents? What if you got 1:1 ratio
of red and black offspring (remember sometimes there can be more than one
possibility)?