An elevator has stopped between the first and second floors of a building. The cable attached to the elevator weighs $6$ kN$/$m and is $40$ meters long. The elevator weighs $10$ kN and there are two persons inside the elevator, weighing $1$ kN each. To rescue the students, the elevator must be manually lifted $5$ meters by pulling the cable at the top of the building. How much work must be done to lift the elevator?

Notes: $-$ All weights are given as forces. $-$ If the elevator is lifted by $1$m$,$ then the length of the cable is $40-1=39$m$.$ Similarly, for every value of the movement of the cable.