Answer:5
Step-by-step explanation: If you look at the base of both triangles, you'll notice that the smaller one has a base of 3, and the bigger one has a base of 6. The smaller triangle is half of the big one, therefore we can safely say that the hypothenuse of the smaller triangle is half of that of the larger one. Half of 10 is 5.
I had the same question on my homework.