The equation for finding the hypotneus of a right triangle is

so we know that 4²+b²=5²
so that would simplify as 16+b=25
so x=25-16
which is 9
so therefore we can conclude that
All of them. 25 is 5 squared, 36 is 6 squared and 48 is 7 squared.
Combine like terms
a^2-4a^2=-3a^2
7a^3+11a^3=18a^3
Then put them back together from greatest exponent to smallest exponent
18^3-3a^2-a