I can't see it fully, but I'm going to assume that it says that DE = DF. Correct me if I am incorrect.
On that note, the questions are actually pretty easy. You already know that DE = 26, and that DE and DF are equal to each other, so DF must also equal 26.
For the second part, when you have an isosceles triangle, and one of the angles is 45º, the other angles are going to be 45º and 90º. Now to write out DEF as a triangle, since we know that DE and DF are equal to each other, that means that D is at the right angle, so angle D would most likely be 90º.
This all resides on the first assumption that I made, but I hope that helps.