Tropical forests are being felled at a rate of 17 million hectares per year, which represents almost two percent of the forest area. Use this informa tion to write a pamphlet describing how much rain forest area exists and when it might be gone .

First you have to figure out if tall pea plants are dominant over short ones. It should say in the question. I'm assuming it is dominant.
So, as you said, one of the pea plants has the genotype of Tt.
The other genotype of the plant must be either Tt, or TT, because it is tall. If it was a short pea plant, it would have the genotype tt, because it is recessive. If they were to reproduce, you would do a Punnett Square.
You could cross Tt with Tt or TT, depending on whether the other plant was heterozygous or homozygous dominant.
If it was Tt and Tt, the probability of it's offspring would be 25% TT, 50% Tt, and 25% tt. Therefore, 75% would be tall, and 25% would be short.
If it was Tt and TT, it's offspring would be 50% TT, and 50% Tt. Therefore, 100% would be tall.

Hope this helps...