Answer:
The distance traveled by the skier is 5.309 km
Solution:
As per the question:
Mass of the skier, m = 64 kg
Coefficient of friction between the ski and the snow, 
Mass of snow, M = 5.0 kg
Now,
To calculate the distance, 's' traveled by the skier, in order to melt 5.0 kg of snow:
We know that:

where
 = coefficient of friction
 = coefficient of friction
N = Normal Reaction
N = mg
Thus
 (1)
                           (1)
Also,
 (2)
                                  (2)   
where
 = Latent Heat of fusion
 = Latent Heat of fusion
Thus from eqn (1) and (2):


s = 5.309 km
 
        
             
        
        
        
We know that speed is a scalar unit while velocity is a vector. The signs are mostly concerned with the magnitude that the car should travel in, the direction is not as important. 
Hope I helped :) 
        
             
        
        
        
ur answer is A or also known as 
When you push a child on a swing, you are doing work on the child because  you are pushing against the force of gravity
hope this helps :)