To find the correct answer, we need to solve for x in the equation x^(5/4) = 243.
First, we can rewrite 243 as 3^5 since 3^5 = 243.
Now the equation becomes x^(5/4) = 3^5.
To solve for x, we need to isolate it. Taking the 4th root on both sides of the equation will allow us to eliminate the exponent 5/4:
(x^(5/4))^(4/5) = (3^5)^(4/5).
This simplifies to x = 3^(5 * 4/5) = 3^4 = 81.
So, the correct answer is D) 81.