Apea plant that comes from a line of true breeding tall plants is crossed with a dwarf pea plant. what are the phenotypes and genotypes of the f1 generation?

All F1 progeny will be heterozygous(Tt) for tall character.  

Explanation:

Ifpea plant that comes from a line of true-breeding tall plants than the genotype of the plant would be TT and when this plant is crossed with dwarf plant who have genotype tt for height trait then all the progeny will be tall phenotypically because all the phenotype would be heterozygous.

                             T       T

                       t   Tt      Tt

                       t    Tt       Tt

So the genotype of all F1 generation offspring would be Tt and phenotype would be tall because all have one dominant allele of tall character.