Question

A pot weighing 4 kg sitting on a windowsill 20 m above the ground. How many Joules is the pot? *

Answer 1

Energy is:$U = m g h$

where: 

$mg$ is the weight;

$h$ is the height relative to a certain reference level (the ground in this case) choosen to have zero Potential Energy.

With your data we get:

$U=(4×9.8N)×20$

$U=784J$