Force, constant speed, friction, acceleration

[daiea08]

I would really appreciate any help on this. I'm confused with this.

Homework Statement

An empty crate is sliding witha speed of 7m/s over a frictionless surface when it hits a rough patch where .25 is the coefficient of kinetic friction. Find the distance it takes to stop the box.

The Attempt at a Solution

Should I calculate acceleration first and if so how do I do the rest of the problem?

 

[cristo]

Hint: Try using energy methods.