Improper because the top is supposed to be lower than the bottom
Answer:
None of those options
Step-by-step explanation:
I just did the work myself and even ran it through a calculator but the correct answer isn't one of those options. Here's my work:

I'd contact you teacher about that...it might be an error in their system (it's happened to me a few times before where the correct answer is marked as incorrect or isn't even an option)
ans=26.92
use trigonometric ratios
a²= b²+c²
a²=25²+10²
a²=625+100
now take square root on both sides
a

a=26.92
a=27 (2decimal place)