The answer is 75% of offspring will be tall and 25% of offspring will be short.
If:
T - the dominant allele for tall trait
t - the recessive allele for short trait
Then:
TT - dominant homozygote (tall)
Tt - heterozygote (tall)
tt - recessive homozygote (short).
In the cross of two heterozygotes Tt x Tt 75% of offspring will be tall and 25% of offspring will be short:
Parental generation: Tt x Tt
Offspring generation: TT Tt Tt tt
Thus, 3 out of 4 (=3/4=75%) offspring are tall (1 TT and 2 Tt) and 1 out of 4 (=1/4=25%) offspring is short. Speaking of genotypes, 1 out of 4 (=1/4=25%) is dominant homozygote (TT), 2 out of 4 (=2/4=50%) is heterozygote (Tt), and 1 out of 4 (=1/4=25%) is recessive homozygote (tt).