a. In the instance where both of the tall plants were Heterozygous (Tt), there would be a 25% chance for a dwarf offspring, with a 50% of a heterozygous offspring and a remaining 25% chance for the offspring to be Homozygous tall
b. No, because both of the dwarf plants are homozygous recessive, which means that if they were both crossed there would be no chance of a heterozygous offspring nor a homozygous tall offspring.