Potential energy of an object is
(object's mass) x (gravity) x (object's height) .
When the oven is 8m above the street, it has
(150 kg) x (9.81 m/s²) x (8 m) = 11,772 kg-m²/s² = 11,772 joules
more potential energy than it has when it's on the street.
That energy has to come from somewhere, so that's
how much work must be done by somebody or something
to raise the oven up there.
