The potential energy that the crate has on the ramp is due to the gravitational force of attraction between the crate and the Earth. It is given by m*g*h, where m is the mass of the crate, g is the acceleration due to gravity and h is the height of the crate.
Here we are given m*g as 500N
The length of the ramp is 5 m and it is inclined at 20 degrees with the horizontal. This can be used to find the height of an object at the edge of the ramp by 5* sin 20.
The potential energy of the crate due to the gravitational force is therefore 500*5* sin 20
=> 2500 * sin 20
=> 855.05 J
The required potential energy is 855.05 J