Answer:

Step-by-step explanation:
Information we have: 
Mass of the sled: 

Spring constant: 

acceleration of the sled: 

We use the formula for the force on a spring (Hooke's Law)

where k is the spring constant and x the distance the mass moved from the equilibrium
and we also use Newton's second Law of motion: 

we combine these two equations:

we solve the last equation for the distance x: 

and substitute the values: 

the negative number means that the mass was moved in the opposite direction that the force, this because the force in a spring is restorative and points towards the equilibrium point