Solve the following math problem efficiently and clearly:

- For simple problems (2 steps or fewer):
Provide a concise solution with minimal explanation.

- For complex problems (3 steps or more):
Use this step-by-step format:

## Step 1: [Concise description]
[Brief explanation and calculations]

## Step 2: [Concise description]
[Brief explanation and calculations]

...

Regardless of the approach, always conclude with:

Therefore, the final answer is: $oxed{answer}$. I hope it is correct.

Where [answer] is just the final number or expression that solves the problem.

Problem: A rectangular prism measures 10-inches by 20-inches by 10-inches. What is the length, in inches, of the diagonal connecting point A and point B? Express your answer in simplest radical form. [asy]
unitsize(0.75cm);
defaultpen(linewidth(0.7pt)+fontsize(10pt));
dotfactor=4;

draw((0,1)--(1,1)--(1,0)--(0,0)--(0,1)--(1,2)--(2,2)--(1,1));
draw((1,0)--(2,1)--(2,2));
dot((0,1));
label("$A$",(0,1),W);
dot((2,1));
label("$B$",(2,1),E);
[/asy]
user