In this case, we have a cross between hybrids Tt xTt so the cross is as follows
Punnet square
Now we obtain frequencies
Genotypic
Tall Homozygous: TT = 1/4 = 25%
Tall Heterozygous: Tt = 2/4 = 50%
Short Homozygous: tt = 1/4 = 25%
Phenotypic
Tall: 3/4 = 75%
Short: 1/4 = 25%