The answer is 5000 ft
His displacement is actually the hypotenuse (c) of the triangle with sides 6 blocks and 8 blocks.
According to the Pythagorean theoreme:
c² = a² + b²
c² = 6² + 8²
c² = 36 + 64
c² = 100
c = √100
c = 10 blocks
Since 1 block is 500ft long, then 10 blocks are 5000 ft long:
1 : 500ft = 10 : x
x = 10 * 500ft / 1 = 5000 ft
The answer is C. Greenwich,England.
Your answers will be A,B,D,
I'm assuming all of (x^2+9) is in the denominator. If that assumption is correct, then,
One possible answer is 
Another possible answer is 
There are many ways to do this. The idea is that when we have f( g(x) ), we basically replace every x in f(x) with g(x)
So in the first example above, we would have

In that third step, g(x) was replaced with x^2+9 since g(x) = x^2+9.
Similar steps will happen with the second example as well (when g(x) = x^2)
The answer is A. Working the formula backwards you get that r^2=256, so r=16