From the arcade to Sams house you can see a right angle triangle:

Across 2 units up 3 units therefore the distance using pythag equals:

2 squared + 3 squared = distance to sams squared

From the arcade to Billys house you can see another right angled triangle:

Across 4 units up 2 units therefore the distance using pythag equals:

4 squared + 2 squared = distance to billys squared

you should get the result from here...