At the top of the ladder the kid has the potential energy. Once he slides down this energy will be converted to kinetic energy and energy to work against friction.
Using the law of conservation of energy;
Potential energy = Kinetic energy+work done against friction
`mgh = 1/2m*v^2+F*S`
`35*9.81*4.5 = 1/2*35*3.3^2+F*4.5`
`F = 301J`
So the work done is 301 J and this work is done against friction.