Help me answering these questions please

In which situations is the principle of cross-cutting relationship useful in determining relative age?

Acertain species of fish can have either long or short fins. the allele for long fins is dominant over the allele for short fins. a heterozygous, long-finned fish is crossed with a homozygous, short-finned fish. of the offspring, will have long fins and be , and will have short fins and be .

Which law represents a balanced chemical equation?