I think I understand even without the picture. I'll add a picture of the Punnett Square filled in, but what you're crossing is
Tt x tt (heterozygous crossed with a homozygous recessive)
The ratio you get in the end is 2 heterozygous (Tt) and 2 homozygous (tt) offspring, so the ratio is 1:1.
So the percentage of offspring that are homozygous recessive is 50%.
Tt x tt (heterozygous crossed with a homozygous recessive)
The ratio you get in the end is 2 heterozygous (Tt) and 2 homozygous (tt) offspring, so the ratio is 1:1.
So the percentage of offspring that are homozygous recessive is 50%.